I did a cold-start of 10.6.2 and checked the Console (all messages) - and still seeing the "kernel WARNING: ACPI_SMC_CtrlLoop::initCPUCtrlLoop - turbo enabled but no turbo P-state found" messages (one for each 'virtual core') that I mentioned in the article last year. (These reportedly will not be seen w/10.6.3.)
And just to see if there was any change - I ran the Core Audio playback test and after appx 15 min, I'm seeing no significant change from before as far as CPU/Core temperatures reported. (Some cores at 80-82C (CPU A - still well under 95C reported limit), CPU A heatsink reported as 62C, CPU A diode temp 73C. IStat menus 2.0's CPU temp reported is the Heatsink, not cores or CPU diode as I mentioned last year in case anyone only uses that vs Temperature Monitor.) And as I noted before, just playing OS X core audio only increases system power draw over 100W from idle based on my UPS' LCD meter. But again my feeling is an SMC or CPU pwr mgmt update would be required to change what I've seen in OS X in that regard. (I forgot to check the booster fan RPM but I suspect as before, it's not really ramping up much over the default rpm. But since it's not an SMC update I didn't expect that to change. I'll do an SMC reset later but doubt it will matter [it didn't]. ) I booted into 10.5.8 (as before) to run the core audio (only) tests, since that's the boot HD I had installed Temperature Monitor, iStat menus, etc on in the past. (Personally I prefer to keep my Snow Leopard boot HD as free of 3rd party extensions/addons as possible.)

At least I've not seen any problems applying the update on this system, although no apparent change that I've noticed so far. (But then none of the change notes apply to me really. Was just hoping there may have been some other changes.)
But YMMV and sometimes the old rule of "if it ain't broke - don't fix it applies" - as it seems no matter what the update, a certain % can have problems with it and regret doing it.

I don't use VM but do have separate (Bootcamp) HDs with Vista and Windows 7. I booted to Vista 64, got a chord tone (i.e. a device detected) but not checked Device mgr to see if any changes seen yet. (Maybe I just moved a USB cable/device to a different port since my last boot to Vista.) HWinfo32 is still reporting 2.92xGHz on all cores at idle/desktop. Not run any stress tests yet to see if they downclock farther than earlier tests, or any other changes but I doubt there are. If any VM users see any benefits let me know. (I only use Windows for entertainment and use bootcamp to run it 'natively' so to speak for max 3D performance. I also booted from the Win 7 Pro HD - no problems seen there so far either. But I didn't expect any really. I've not run any benchmarks yet but performance has been very good overall in the past - no complaints in any of the 4 OS's (10.5.8/10.6.2/Vista 64bit Ult/Win 7 Pro 64bit) used with this machine. Exact same Win7 Exp. test scores, but that's not much of a benchmark.)

For other 2009 Mac Pro owners that apply it, let me know if you see any pros or cons. Especially anyone using VM, XP or that has seen stability problems in the past, as the change notes imply improvements in those areas. (I didn't have any stability issues before the update personally. No KP's, no thermal shutdowns, etc. even in heavy use like HB encoding (all cores loaded) for many hours a day at times.) But I don't run VM nor XP.
Update: A Quad-Core (single cpu) 2.66GHz owner that uses VM/Win XP wrote:

"Applied update with no issues. Everything appears stable. VM Virtual Box (freeware) up and running WinXP with no problems - here I noticed what appears to be a huge decrease in boot time - not that it really was slow to begin with - and not sure if such an update would cause this...
-Lawrence"

Several other reports of no problems with the update (nor any before) but no noticeable difference (but no mention of VM use, XP, etc.
BTW - I've seen some posts in Apple's forums from owners that were not aware of the fact firmware updates won't work if run from RAIDed boot drives. (Again this was noted here years ago.) One Mac Pro owner with RAIDed boot drives said used a bootable Firewire HD to apply the update, but still had to remove his RAIDed internal HDs for it to complete.

"About Mac Pro EFI Firmware Update 1.4
This update addresses the following issues for Mac Pro (Early 2009) computers:

• Improves compatibility with virtualization products utilizing VT-d
• Improves storage performance under Windows XP for Boot Camp users
• Improves system reliability during the boot process

To complete the firmware update process, please follow the instructions in the updater application (/Applications/Utilities/MacPro EFI Firmware Update.app). The updater will launch automatically when the installation is complete.

For more information about firmware updates for Intel-based Macs, please visit: http://support.apple.com/kb/HT1557 ("About firmware updates for Intel-based Macs")
(OS X) System requirements: 10.5.8 or 10.6.2"

None of the above applies to me (I don't use VM, nor XP, and have seen no boot or stability issues with my system.) But since Apple doesn't always list every change/fix and as an owner that's seen the higher than expected CPU/core temperatures from simple OS X Core Audio playback (100w+ power usage rise from that alone) and missing turbo p-state support boot log errors, I wondered if the update would have any effect on that. (It doesn't - same error messages seen in cold boot 10.6.2 log, same 100W+ increase over idle just by playing audio in OS X, etc. But reportedly with 10.6.3 beta the no longer appear - not sure if just suppressed perhaps. I was expecting an SMC related update or OS X pwr mgmt file perhaps to address the OS X Core Audio temperature/wattage ramp up. Not that I've seen any problems from that - but audio only playback in windows shows only a few W increase over idle draw.)
I was almost leery of applying this on 2009 dual 2.66GHz CPU system as none of the change list 'fixes' seemed to affect me, but decided to be a guinea pig. Downloaded the updater and Firmware Restore CD 1.8.
For any 2009 Mac Pro owners that apply it, let me know if you see any pros or cons - especially anyone using VM, XP or that has seen stability problems in the past. [See later post above for my initial notes after the update - I've seen no real change in that regard on my 8-core 2.66GHz system.]

Here's the page/info on the 2009 Xserve EFI firmware update:

"About Xserve EFI Firmware Update 1.2
This update addresses the following issues for Xserve (Early 2009) computers:

• Improves compatibility with virtualization products utilizing VT-d
• Improves system reliability during the boot process

If you will be doing headless updating please visit: http://support.apple.com/kb/HT3962 ("Xserve (Early 2009): Applying EFI firmware update to a "headless" Xserve")
For more information about firmware updates for Intel-based Macs, please visit: http://support.apple.com/kb/HT1557"

There's also a doc About EFI firmware updates for Xserve.
And here's the link to the download page for Firmware Restoration CD 1.8. (Download requires accepting license agreement)

"About Unitor Family Driver 2.5
This update addresses isolated reliability issues, especially when using multiple Unitors.
The Unitor driver supports the following MIDI interfaces:

Unitor8

AMT8

MT4

System Requirements: OS X 10.5.7 (or later I assume)"

" In regard to the script for the Blue-ray drive: I posted a message on the Mac Rumors forums about a week ago, asking for help in script writing for the Pioneer Blue-ray/DVD drive. Someone just replied today. The script suggested was:

on idle
do shell script "drutil info"
return 28 (return 120 also works - see below)
end idle

Save as an application and check the stay open option.

I tried it on my machine a Macbook Pro, and it runs and quits when you tell it to do so. I will ask Mike M. (one of the owners with this problem that disabling ES sleep and previous scripts didn't help (original script required force quit, revised script that worked for one reader didn't for him) to test it and see if it works to keep the drive visible. You might want to forward this to Iain (who had sent earlier script examples here) for his reference.
I will get back to you when I get confirmation that it does work as expected.
(Update (Jan 21st, 2010):
The script noted (above) does work, as does one modified by Iain (another one sent in Jan 18th, 2010) using "return 120" instead of "return 28". Evidently polling to drive once every 2 minutes is enough to keep it connected.
Best regards, David"

Also added the above script to the Dec archives page post that had the earlier scripts.

• About liquid contact indicators (LCI) on portable and desktop computers ('Affected models' lists only some late 2008 and later Macbook/Pro (13 and 15in models) - but text mentions some desktop keyboards also. Latest model keyboards I assume)
• Mac OS X keyboard shortcuts
• Copying iTunes Store purchases from your iPod or iPhone to a computer
• Adding and Deleting Songs and playlists from your iPod
• How to copy previously-burned DVD-R video discs
• How to disinfect the Apple internal or external keyboard, trackpad, and mouse
• iTunes for Windows Vista or Windows 7: Troubleshooting unexpected quits, freezes, or launch issues
• iTunes for Windows XP: Troubleshooting unexpected quits, freezes, or launch issues
• iPod touch not recognized in iTunes for Windows

• Apple officially announces January 27 event
• Apple to launch 22-inch touch-enabled all-in-one PC in 2010, says paper
• Apple Launching 22-Inch Touch Computer This Year, Says Chinese Report
• Can Apple make tablets catch on?
• HP, Dell offer 3G in laptops, so why not Apple?
• Nokia hits back at Apple patent claim
• Apple seeks ban on U.S. Nokia imports
• Aliph Jawbone Icon: a Bluetooth Headset You'll Want to Wear (Really!)
• AT&T Announces New Unlimited Plans
  
  Apps and Misc. Software Updates: (later added first)
• apprelief.com (App developers donating profits from sales to Red Cross/Haiti relief fund)
• Apple Approves Grand Theft Auto: Chinatown Wars for iPhone
• Posterino 1.6.3
• VueScan 8.6.03
• MPlayerX 0.9.6
• Firefox 3.6rc2
• Wings 3D 1.2 (free 3D modeler)
• GrandPerspective 1.3.0
• SwitchResX 4.1.1
• jalada Ultimate Racing 1.2.1
• Free Dragon app for iPhone, iPod Touch nails dictation
• Yelp's iPhone app gets check-ins, friend stalking

• January 2010 UDK (free Unreal Development Kit) Beta and build notes
• Nvidia releases details of Fermi GF100 chip
• Intel i7 Extreme 920XM w/NVIDIA GTX 280M Performance Review - Breaking the Mobile Speed Barrier
• Microsoft releases IE6 flaw fix (Why is anyone still using it?)
• Mass Effect 2 DLC Might Be Free
• AT&T Glitch Reveals Private Information
• Network flaw causes scary Web error (ATT)
• Mobile donations to Haiti exceed all in 2009
• x264 HD Benchmark 3.0
• Wii board helps physios strike a balance after strokes
• Lenovo ThinkPad Edge (short review)
• Conan using 'Tonight Show' site for eBay sales
• BMW adds new engine and tweaks 3 Series coupe and convertible