I had a laptop under one of their warranties (laptops aren't worth the trouble to fix myself) that, after about six months of using it, would randomly not see its CDROM drive.
After coming back from being deployed with it I sent the thing in for repairs. It came back CND (can not duplicate). Next TDY, it did the same thing. Again I took it in, again it came back CND. Not too long after getting it back for the second time the damn thing started acting up again.
So this time when I take it in I have the tech at the counter try it and low and behold the thing doesn't read. I have he make sure to note it on the ticket that this isn't just my vivid imagination, but the thing is actually broken. When it comes back CND the third time (each time taking around three weeks) I have them fire it up at the service counter and what do you know, the CDROM doesn't read.
So I tell them I would like it replaced under the warranty's three repair lemon rule. The manager's answer, "we can't do that because each time the depot marked it CND, they never actually repaired it three times."
Needless to say I was less than happy with that answer. After a few days on the phone to everyone in the Best Buy food chain that would listen they finally decided to "do me a favor" and replace the laptop.
That's the last major purchase I have made there. That and me telling my wife that next time the sensor on the door goes off I'm breaking into a run out of the place, just for fun, has lead to me shopping there much less.