I have to admit, since getting Vista Business (free via MSDN for training/testing/development etc only, I sure as hell wouldn't be buying it) it's actually been surprisingly pleasant. A *lot* of improvements over XP (mainly because XP had so many stupid design decisions to begin with), perfect example being that if you type a web address into an explorer window it now opens the web page in your default browser -- in my case Firefox. The new interface is also reasonably usable, if you switch back to classic start menu and classic view for things like the control panel. Compare that with XP's Luna which had me running back to classic theme within minutes. I also like the way it automatically asks for authentication as required, rather than having to use secondary logon (run as...) all the time -- as *nix and OS X have been doing for ages.
I was very surprised to discover they've omitted a lot of the guff that used to be very difficult to remove, for example messenger isn't actually installed and instead the link in the start menu takes you to a download page.
One caveat is that they've changed the authentication standard for SMB/CIFS which now defaults to NTLMv2, causing my samba shares to fail inexplicably. All that was required to fix that one was a group policy object change allowing auto negotiation of both NTLMv1 and v2, but it wasn't exactly obvious. For those of you interested --
read more here.
Saying that I'm posting this from OS X 10.4.8 -- go figure