These things kill me.
Don't get me wrong, I actually think they're incredibly genius. You can talk all you want and still have your hands free at all times.
My favorite, though, is when some student is walking around campus with one of these babies on their ear. You can never tell if 1) they're talking on the phone, 2) they're talking to you, or 3) they're just crazy.
I just had such a run-in. It left me very confused.