Excellent...stable, awesome interface, polished (even for a RC). Cant wait to see what the final release is going to look like.
One complaint: We have a lot of older software here at work, and some of the old DOS based programs don't seem to work, even in compatibility mode. We'll just have to work with the vendors and see if we can get updates or something.
Best... yes, we all think that windows 7 is great and the best, etc, but it's impossible to make an excellent OS that works with no errors, so if excellent is better than best, i'm still waiting for an excellent os.
Windows 7 is very fast and stable on my old dinosaur of a computer. However it still won't recognize 4 of my 8 USB ports. I reported it as soon as I started using Build 7000 but the problem is still there.
The only other thing is that I still want the Classic Start Menu back. I'm sure that something will come along where I can have it at some time. I'm not worried about it.
Update: I set up the Unawave thing. It's really pretty awesome.