One of my main groups has switched over to 4th Ed, and we've really enjoyed it so far; fast-paced action, tricky tactics, and lots of teamwork.
Also have another group that is running a heavily-modified 3.5 Faerun game, and a converted 4E Midnight game.
Just started running the Scales of War adventure path with the caveat that almost everything produced for 4E is good to go. Interesting stuff out of that one so far!
So yeah, a pretty big conversion to 4th Ed, but still sticking with some tried-and-true...I'd like to get out of the box a little more (a friend owns the Reign system and I really want to give that a try), but eh, what can you do?