I'm running Win7 on 2 PC's so far.
1. 2.0 Ghz P4 HT, 2 gigs slow ass ram, Geforce 2 (woot!)
2. Eee PC 904HA 1.6 ghz atom, 2 gigs, intel 950 gma.
So I haven't been trying out any high end games with the video card etc.. but I've had Win7 for about a week + now.
FAST. MUCH faster than windows. Going from XP on my Eee PC to Win7 brought almost no performance loss.
There are quite a few things that are obvious improvements to the Windows platform in Windows 7, most of them are implemented very well but some are still a bit, well confusing.
Libraries would be a great example, not very straight forward and really frustrating until you actually understand that it's actually something other than a normal folder.
After that though, it's great.
Streaming video actually works better on my Eee with Win7, though stored video playback (@ around 720p) needs a second to load even with VLC
Networking and networked storage is muccch better. Right after the initial install Windows 7 already had identified my networked devices and accessing them was as painless as it has ever been.
There are more than a few other things but they are documented well as features already so I won't waste my time.
With laptops lookout though! My Eee PC's battery life dropped an incredible 20 percent, and wifi connectivity is poor (connections I could pick up in my corner of the office with Ubuntu or even XP are no longer accessible unless I go hide in the corner.)
That being said, my impression of Win7 is that windows finally delivered again with something on the level of XP. It really is Vista improved and at XP speed.
I would of course wait to install it as a primary OS, but if you have a comp lying around, I'd encourage you to do it.
Btw: I've installed just about EVERY old game that worked on XP, and just about every program I've tried has worked flawlessly and without error. I have yet to crash or have any real notable issues with the OS to this date.