I had the opportunity to go to one of Microsoft's "Roll out events" last month in Sacramento. Got to see Vista "up close and personal" so to speak, but on a machine that was optimized for it...I REALLY like some of the "eye candy" improvments they've added to the new OS, as well as some of the new functionality, BUT, I won't make the change for a year or so, to give manufacturers time to get good solid drivers for various hardware. I'm relatively happy with my current system, and am NOT ready to dump $1000 into rebuilding it AGAIN just yet... I spoke to one of the MS reps and he said 6 months minimum, maybe 1 year, and that seems just about right.
Be sure you have LOTS of system memory, as Vista is quite a resource hog...I have 1.5 Gb, and is barely enough...I'd recommend 2 gigs MINIMUM for Vista if you plan on doing anything that is graphically intense. (games, photo editing, graphics design, AutoCad, etc.)