Some people report having success with Vista, but as a bit of a nerd with a few legacy apps to run, I have to say I wouldn't touch it with a forty foot pole.
My wife uses it and it took me several days to get Quickbooks running on her machine. Admittedly it was an older version of Quickbooks, but her boss (my father-in-law) didn't want to upgrade (fair enough, too!), so I had a royal fight on my hands.
I work in IT (with plenty of experience as a software developer and in tech support), and at least until SP2 I won't even consider using Vista. It is slow (even with 1GB of memory and NO applications open) and broken (won't run a lot software or talk to a lot of hardware).
Why else would Dell be allowing people to order their machines with XP still? They went Vista-only at first, but obviously everyone wanted XP back.