My MBPr charger cord frayed from regular wear and tear. These things are built to last really only 1 or 2 years from just regular use, even when you don't use the fold out flaps that come with it (I hadn't). I called this store and asked about possible replacement; the employee stated that if I simply brought in the charger to their store they'd see what they could do.
I'm happy to report that they replaced the entire thing for free! Brand new charger, and no hassle at all. I gotta say these guys are great. Definitely going to keep me as a customer. I don't even write reviews, but these guys definitely earned this one. Keep up the good work, Apple.