I've been running it for a few days now and it seems to work well enough for me to stop using Firefox (for now). It still hangs up for a few seconds every once in a while but nothing like the multiple-minute lockups that Beta 2 having. Also, they seem to have fixed the annoying issue with web forms (like the one I am using for this post) not refreshing properly. Even when I was complaining about Beta 2, I knew that IE7 was going to end up being really, really good and I'm happy to see progress is being made.
I'm just delighted to have a browser where I can run it under multiple threads and still have tabbed browsing. I have noticed that memory usage seems to be a fair bit higher that IE6 but not nearly as much as Firefox uses because of the way it stores old pages in memory by default.