Windows 7 is definitely a good OS

.
Performance - slightly slower then Vista on test machine (this is an older machine mind you)
Boot Up - Slower then Vista (again been an older system gotta give it leeway there)
UI - Very nice, loving the "Superbar", the overall UI seems cleaner and more consistant then Vista overall (but still few issues here and there, like the iconless toolbars!)
Overall - Shaping up very nicely, the smaller install size (half the size of my Vista install) is definitely nice. While it did seem slower then Vista and I have to admit had some mouse issues and the UI was a bit sluggish at times, I think that was more because of the test machine then 7, as in my VM copy the performance increase was very noticeable! (VM 7 can run on less RAM and is considerably faster then VM Vista).