Oh, and yeah, I forgot one important point in my last comment: the hardware support. After I installed Win7, it found all my hardware and installed drivers for it. All: network, sound, video - was working. I installed the correct drivers from my hardware manufacturers anyway, but it's still nice, remembering XP days, when I had to go through the pain of looking drivers for my network and sound card.
I have Windows 7 Ultimate 64bit, just build a new comp - and I love it so far. Everything just seems faster and older programs run fine too. If you have a new hardware - I say go for Windows 7!
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