I've got a Cervélo road bike that I've only had a few years, and the carbon dropout is worn out so badly that on my last ride the rear wheel came loose under load and the tire rubbed the chain stay. I took it to a dealer who filed a warranty claim, and their warranty rep got back to their mechanic and said they wouldn't honor it, as it was something I must've done to cause the wear. I asked the mechanic what that could've been and he said, hesitantly, that maybe I didn't tighten the QR on the axle enough. I am very diligent about things like that, and there's absolutely no way I rode with the axle loose enough to do that, let alone long enough for it to do that. In fact, the sales person at the shop I bought it from actually went over what not to tighten too much and what not to under-tighten and all of those kinds of things with me because I was on the fence about a carbon frame in the first place. The mechanic at the dealer said he believed me and he'd try and push back with the warranty rep for me, but he wasn't hopeful. I feel like the warranty rep saw the proof of purchase, saw it was from a shop that isn't even a dealer anymore and realized I'd had to go to another shop, and saw that I got the bike at a "closeout" price anyway, so decided to just write me off.