My decent gaming computer I got came with Vista Ultimate, and I had some strange problems with especially graphics, and some games wouldn't run well that should have since I had very close the recommended specifications. I got Windows 7 for the student price, and have had absolutely no problems
at all. Vista had some odd quirks, but nothing as bad as most people say it is.
Two odd examples of my graphics differences with Vista to 7. Keep in mind the
only change was I did a clean install of 7 on the exact same hardware, same latest drivers and DirectX.
My girlfriend plays The Sims 2
alot, and whenever it snowed heavy on Vista Ultimate, all the ground textures would flash purple, indicating bad textures or something graphics. Now on 7, it runs absolutely fine...
I tried the Batman Arkham Asylum (AWESOME game btw) demo on Vista, and I couldn't even run the menu in
lowest detail. Now on 7, I can run the full game on
very high with not a single slow-down...
I've definitely noticed a speed improvement, I'd even say from XP (which I still like as well for my other computers). I love the taskbar, and really there wasn't much I had to configure to get the whole OS to run exactly how I want it; Vista I spent like a half hour tinkering with some things. Also the virtual XP mode is kinda cool... Oh, and you can place gadgets anywhere on the desktop instead of just pinned to one side of the screen.
Another neat feature I've read about (but not had to experience) is apparently if Windows denies you from deleting or doing something with a file because of it being 'used by another process', it apparently tells you
what process (!!!!

)
Not had a single problem with my Windows 7 for over a month.