I wiped a 3GS, installed iOS 5, and restored my son's apps and data.
I did it primarily to get iMessage - part of our assault on AT&T.
It's better than I thought. I expected more UI problems. I'm sure there are problems, but I expect those will improve with later versions of iOS 5.
If you have a 3GS I think it's worthwhile, but I'd wait until 5.1.