First off, I'm an OSX guy.

I put Win 7 beta on my Macbook and ran it with Virtual Box off of a USB HDD. It was VERY fast, even faster than a T41 Thinkpad.

Then I ran Win 7 on a Dell Mini 9, which also dual booted OSX. Win 7 was VERY impressive on an Atom. Win 7 is a VERY good OS IMHO.