How does it perform and is it a step up from XP or not?
More like two steps up, 6 steps sideways and five steps back. :-?
advantages: It's 'pretty' (arguably), it's more secure (but very in-your-face while doing things), and above all it's very different.
On machines with identical hardware, XP will blow it out of the water speed-wise.
Certain trivial things take absolute *insane* amounts of times. Copying files over a network or expanding a large zip file can take ~50 times as long under vista than they did under XP - a quick google search will show you tons of rants from people about those issues. (I had a 500MB zip file myself that took 2 minutes to unzip under XP, and well over an hour on vista -- absolutely ridiculous!)
Bottom line: personally, the only reason I'd even remotely consider Vista would be for compatibility testing of any software I might create, but the way things look right now I fully anticipate using XP until it's end-of-life in 2014... Barring any major changes in Vista, of course.
for normal day-to-day use there is surprisingly little incentive to use Vista, and many reasons not to.
I guess 5 billion dollar of development money doesn't buy what it used to. :-?