My experience with this--
My back glass had a small ding in the Apple logo that was really bugging me. I took it in and asked if it was true that they would replace the back glass for $29. They gave me a little attitude and acted like they didn't have any in stock, but the guy came back from the back room with my iPhone already installed with new back glass. I handed him $30 in cash, and he said, "No charge, but next time they'll probably charge you the $29."
The three or four times I've had to go into the Apple store, they've always exceeded my expectation of what the outcome would be. My Apple hate is fading more and more with each passing day.