I work as I.T. for a small company with about 150 computers, including a small server farm.
There are only two Vista computers in the company, the CEO's laptop (he hates it) and a Vista test computer. I hate Vista with a vengence. It will turn a relatively fast computer into a boat anchor - it is a memory hog and very sloppily coded. The ultimate in MS bloatware. Wost of all, all the administrative functions have been dumbed-down to the point of stupidity, many hidden deeply or reconfigured to the point of unrecognizability. Tons of arbitrary paradigm changes and lots of questionable ergonomic choices...
I've had the opportunity to test the most recent release candidate of Windows 7 and it benches about the same as Vista with a couple of tweaks and different window dressing. Not impressed at all.
I'm keeping the company on XP for the forseeable future. It is stable and very lean and fast - especially when compared to Vista.
At home I have 5 pcs 3 of which are running Win XP and two of which are running Ubuntu Linux.