I've been running Win7 Ult x64 for at least a month now. It's been running very smooth. I didn't have to install any drivers after install, and I haven't had any issues with it at all.

I always turn off UAC so I haven't had any issues with that. All the software I use runs smooth, the UI is nice, it doesn't lag, it doesn't glitch, I've not had one lock up caused by windows, no errors. It's been a smooth migration from XP to Win7. It was a clean install, I'm just installing what i need as I go along.