My biggest frustration with Vista is the large number of user interface changes compared with the XP way of doing things.
MSFT are apparently convinced that every single one of those changes is a change for the better. I have gone through the retraining requirements with several clients (for both Vista and Office 2007) and we were not happy with what we came up with.
For home users - great, buy Vista, get more eye candy, get some new GUI features. A no-brainer (at least if you're a fan of eye candy).
For business - "Hello Help-Desk, where has the the File menu gone in Word? How do I do a 'Save As' now?"
Most big businesses seem to use Windows XP with the 'Classic' UI rather than the 'XP' UI. I'm guessing many of them will want to use Vista with the 'Classic' UI too - which leaves with you with... err... XP with a few extra bits, just slower?