Two days ago my Mac refused to power up. Strange - it was charging just fine before! I was at work and it did not seem to be a problem with the wall outlet, so I checked when I got home and, sure enough, Jody's power brick worked to charge it up but mine was busted.
I was very fortunate to grab the last open Genius Bar slot this evening, where the Apple tech confirmed, "Your power adapter is non-functioning." And then he ran another test to make sure it was not the battery, his eyes flicking back and forth between my Mac and his. Mine is now out of warranty (it's from the first batch of aluminum 13" models they made in late 2008) but... Mr. Genius said, "I'm going to make an exception and give you a new power adapter."
Yay! Thanks, Apple! You made my day.