Here's a simple iPhone fix that others may appreciate. A few weeks ago my microphone started to cut out — I could listen to music over the headphones, but with both pairs of earbuds the microphone would cut out, and disconnecting and reconnecting them would cause the call to drop. I finally took it to the Genius Bar today and they immediately took out an otoscope and discovered that the hole where the headphone jack fits in was filled with pocket lint! One quick burst of compressed air later and it was working perfectly again! (Apparently they get this problem a lot, as they've got a special mini-jack attachment for their compressed air can.)
A nice side effect was he noticed the screen's hairline crack I'd gotten when the phone fell out of my pocket. From all I'd read on the Net I thought I'd have to pay $250 to have that repaired, but he said so long as it was just a single hairline crack and there was no damage to the case itself they could do a warranty replacement — five minutes later I was walking out of the store with a fresh-out-of-the-box iPhone.