Well, after posting the message blow, I decided to give a good look at my 16gig Black iPhone (bought on launch). I think there's a crack between the speaker and chrome. Very tiny, and practically invisible unless you cause light reflections to move back and forth across. I still need to take a macro photo when I get home to be sure.
I recall someone spotting cracks on their white iPhone the moment he took it out of the box at home. When he went back to the store they accused him of dropping it and wouldn't exchange it or something.