I was told early on to stay away from Vista, as it was purported to be riddled with problems. Since I already had XP, I figured, "if it ain't broke, don't fix it!"
I just bought a new computer for my assistant last week, and it of course had Vista on it. It seems to work just fine (maybe they needed a few months to get the kinks worked out of it). Having said that, the word on the street is that it is not very network-friendly-- but, again, my assistant's computer is on a network here at work, and, so far, no problems...
I was impressed enough by seeing it on my assistant's computer to go ahead and install it over XP on my home computer. I like the look and feel of it, but I noticed my Outlook email client is now bogging down considerably-- it even crashes on me from time to time. I can think of no other reason as to why Outlook would not perform the way it usually has, other than some glitches in Vista, since it worked fine over XP. I imagine they'll set up patches for that as Vista matures in the marketplace.