I have been using IE 7 for a while now. I used beta 1 and now am using beta 2.
I like the new look of beta 2, but some of the icons aren't that obvious. You have to go searching to find the refresh and stop buttons. Favourties are not obvious either.
Hopefully some more thought will be put into this before the finished version.
Tabbed browsing is great, although has been around a while in Firefox, Opera and others.
One thing they I think haven't got right in IE 7 that Opera does well:
links that open a new window open to a new tab in Opera, in IE 7 it still opens to a new window.
Other than that it looks like a good step forward for IE.