I switched to seven mainly because the more and more new hardware has less if any xp drovers/support I couldn't get my audio to work plus my xp install was old and really really messed up it could things like sync music or run programs without warning messages.
I have a Foxconn destroyer, and black edition AMD 940, 4gigs skill ram and a not so good xfx9600gt it's not super cutting edge but better than a dual core socket 939. I switched to windows 7 63bit from xp32 bit and damn program installs run fast I run all kinds of crap at once I haven’t tried running 2 games at the same time well with one minimized but, I bet it would. I love snapping back into windows while running games without waiting and on top of this I haven’t even started OCing yet.
Hell my ram is 1066 running at 800.
I have to say having all 64 bits utilized speed performance plus xp saw only 3.25 gigs of ram. Seven only uses ½ of my ram doing casual thing with say gta4 running in the background it a little over half my ram being used.
The only problem I have is with old 2d games Starcraft FO yatayata it cause a rainbow effect till I get in game except for fallout has a little bit of rainbow in game. On this note I want to try the new f2 resolution patch.