Wirelessly posted (iPhone 4: Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_3 like Mac OS X; en-us) AppleWebKit/534.32 (KHTML, like Gecko) Version/5.0.2 Mobile/8F190 Safari/6533.18.5)
It's probably the best first beta Apple have ever released from a stability and compatibility with 3rd party apps perspective. Having said that, there are issues with it as you'd expect. The main ones I've found are various animation glitches, major problems with home sharing to the iOS device and some problems with mail (unread counts being wrong, mail body not downloading straight away, and it also suddenly showed me as having two MobileMe accounts which I could only fix by removing and re-adding MobileMe).
Personally, I can put up with the issues and use it day to day, but that might not be the case for everyone.