i started using vista ultimate 64 the first day it was available and the ONLY problem i had was a lack of 64-bit drivers for my HP laser printer. once HP supplied those, vista was golden. not once did i have an issue while using vista was it the fault of the OS. since i install and 'test' beta software, i expected there to be issues once in a great while after installing said beta software. that wasn't the fault of vista!
now, as for windows 7, i've been using it for months. i joined technet back in august just so i could get the RTM build of windows 7. again, i've had ZERO issues with win7. windows stay resized and in place. all applications run smoothly. EVERYTHING works as advertised. i've also installed win7 (upgrade, retail, oem, technet) on numerous machines (desktop, laptop, netbook) and so far, the only problem i've encountered has been with a verizon wireless network feature on a dell laptop. after calling dell and getting a hidden link to a software upgrade, even it works flawlessly.
yes, i've had to reinstall win7 since august but that was due to my hdd crashing. you can't blame win7 for that.
edit: there was one other issue.......a linksys wireless router didn't want to work with win7. after upgrading the firmware for it, everything is fine and dandy. (talk about tracking down and borrowing a laptop with xp on it in order to get the firmware update! i ended up borrowing a netbook from a local cell phone office)