To be fair XCNuse IS right, Vista seems to do some sort of program cacheing that makes it use a scary amount of RAM doing "nothing", but from what i've read it DOES release this RAM when it's doing something that needs the extra RAM.
Currently Vista's using 999 MB of RAM with a 148 MB Firefox window, an 80 MB Firefox/Pandora windows, Teamspeak (4 MB), Messenger (7 MB), Profiler (1.6 MB), AVG (Roughly 2 MB) and about 3 mb of other Random crap. So far every service is at default EXCEPT ReadyBoost which is disabled on account of gaining 500 MB of "Disk Cache" on a Pen Drive was costing me almost 100 MB of 1337 Ballistix RAM.
It's NO quicker than XP in operation, but it does boot a little quicker and appear to be more stable. Aero is nice, Flip3D is UTTERLY pointless (at least i've used it once and gone "wow thats nice" and then just used Alt+Tab 'cause it's quicker), the little "Document Preview" if you hover over an icon on the taskbar is nice (esp seeing as it works for stuff like LFS with great framerates, the Sidebar is nice but doesn't do anything for me personally.
"UAC" is a fecking PITA ("Hey, you double clicked an icon, are you SURE you want to do that"? "Yes! Thats why i double clicked it!" "Hey, a programs trying to run - are you SURE you opened this program?" "YES!" "This program wants to open. Will you let it?" {UAC DISABLED} :P), useful for n00bs, but tbh even THEY will get annoyed and turn it off.
You don't need a great PC for Vista but you WILL want 2 GB of RAM - it doesn't use much CPU (even with all my crap open i'm using 3% of my CPU) but it DOES use a lot of RAM.
/me goes hunting for services.