Well, I had my 360 for about 4 months when I got it replaced. It kept freezing when I played Oblivion. I got it replaced at Best Buy, brought it home, same problems. Got Oblivion replaced, same problem. Got a new 360, same problem. Got Xbox Live, got an updated patch, problem solved.
All those 360's I trashed were probably in perfect condition, but I got all my stuff for free just by driving down to Best Buy.