Upgraded from Vista Home Premium 64-bit to Win 7 HP 64.
Slightly funny story: Received the package in the mail (I always want the hard copy), opened it, and read on the disk: 32-bit Version. Having pre-ordered it some time ago I'd forgotten the "both versions included" part of the deal, I thought I'd been given the wrong version! Oh no! I searched MS help, found a phone number, called and explained my dilemma, the guy apparently was going to send me a new package when I found the one teensy box on the package that said, "Includes both 32-bit and 64-bit versions." Oh yeah, I sorta remember that -- The 64-bit disk was UNDER the 32-bit one. Uh, sir, uh ... nevermind.
The install didn't go perfectly, 7 found some items that weren't compatible but didn't make it entirely clear that those items had to be manually disabled before the install could proceed (I didn't need those items anyway so, no big deal). Once I figured that out it went swimmingly, but took longer than I expected. Not longer than they SAID it would take, but I didn't believe it would take as long as that. It did.
Works great (as did Vista). Vista would occasionally choke on one program or another, but always recovered gracefully, haven't had any glitches yet in 7. 7 uses FAR less memory, from 36% at idle in Vista to ~25% in 7. I never ran low with Vista (I have more than 4 Gig, hence the 64-bit version), now I KNOW I won't run low with 7.
Nitpicks; SO much faster in some regards it's unmanageable. For example, if the cursor so much as glances on another window, that window comes immediately to the forefront, whether that was my intent or not (is there a workaround, like menu-delay in past versions?). Had to change my decade-old Alt+Tab habit to WindowsKey+Tab because Alt+Tab is entirely unuseable; Changing another habit, the Start menu, to using the task bar instead was easy enough, but I LIKED the Start menu.
Otherwise, works as well as Vista (again, I never had issues with Vista), uses less memory, changes are easy to learn -- What's NOT to like?