I returned mine and went back to the 3GS. I will wait till Apple secretly updates their antenna with an invisible coating (or whatever it is you know they're going to do).
I miss the hi-res screen and better battery life. But my 3GS is unlocked and jailbroken, and to be honest I really like the backgrounder app better than iOS4's multi-tasking capabilities. I also enjoy not being terrified about placing the phone on a glass table for fear of scratching it, or shattering the glass because it's the same tensile strength, or any of that other BS.
Signal quality seems better on my 3GS. I'm left-handed so it's probably more pronounced for me.
Throughout all of this, Apple's customer service has been extremely understanding, and I will definitely buy from them again, so long as they find a muzzle to put on their CEO so he doesn't continue to alienate his customer base.