"Combo updater stealth updated
I'm noting that people who downloaded combo updater of 10.7.3 in more recent days are getting a new OS X build number. 11D50b where as people who downloaded it longer ago only have 11D50.

What's different is hard to say, as the combo updater wasn't even plagued by the bugs the delta/software update versions had to begin with, yet they still felt a need to revise the combo updater (and didn't announce or advertise it either, in fact anyone on a 11D50 system isn't prompted by software update that they are not current despite there being a revised build).
In any case, i thought it worth noting the existence of the 11D50b build.
-Adam W."

Not sure if anything's functionally different, maybe an installer bugfix? (The Combo D/L Page dates were not changed and no 'v1.1' designation as with the revised Security Update for Snow Leopard, although they didn't chg those page dates either.)
(Due to many reported problems Apple had pulled the 10.7.3 (Delta) updaters from their D/L page and the original links for the Delta Updates are redirected to the Combo versions for both 10.7.3 Client Combo and 10.7.3 Server Combo.)
I'm not using Lion (yet) but if anyone knows what's changed or had better luck with the 'b' build vs the original Combo install, let me know the details. Thanks.
  

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"About MacBook Air EFI Firmware Update 2.3
This update enables Lion Recovery from an Internet connection on MacBook Air (Late 2010) models and addresses an issue where the system could restart if the power button is pressed immediately after waking from deep sleep.
For more information about Lion Recovery, please visit: www.apple.com/macosx/recovery/
System Requirements: OS X Lion 10.7.3 and later"

Per Apple doc, EFI version after update should be MBA31.0061.B07.
  

"About iMac EFI Firmware Update 1.8
This update enables Lion Recovery from an Internet connection on iMac (Mid 2010) models.
System Requirements: OS X Lion 10.7.3"

Per Apple doc, EFI version after update should be IM112.0057.B01.
  

"About MacBook Pro EFI Firmware Update 2.6
This update enables Lion Recovery from an Internet connection on MacBook Pro (Early 2010) models.
System Requirements: OS X Lion 10.7.3 and later "

Per Apple doc, EFI version after update is MBP61.0057.B0F. (IDs are MacBookPro6,1 and MacBookPro6,2)

There was an EFI update posted Jan 23rd to add Lion Internet recovery for the 13-inch Mid-2010 model (EFI Update 2.5). (As of tonight that D/L page still has not been corrected for MBP rom ver.)

  

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• About the "Apple Hardware Test does not support this machine" message
• EFI and SMC firmware updates for Intel-based Macs
• iCloud: Setting up and using Back to My Mac with an 802.11n-based AirPort base station, or Time Capsule
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