I'm on my second...the first one got stuck at the Apple USB logo screen and would not go further when restoring. Even the guy at the Apple store couldn't get it to work.
On my 2nd iPhone 4. 1st one had really bad reception issues and the proximity sensor issue. I'm happy with the 2nd one. Reception is much better and battery life seems to be better as well. I still have the sensor problem even with upgrading to 4.1 although it's not as bad as before.