for what it's worth, i have yet to see a disc error in the three months i've owned my 360, and i could count the lockups on one hand. mine's been damn near perfect so far, and it's one of the original units (built on 11/6). it shouldn't be an issue with Burnout either unless you happened to get a faulty disc. i've logged a ridiculous number of hours in that game already without a single fault...fantastic game
if you do send your unit to MS, you will be able to retrieve your profile...but you'll lose any stored game data/saves that are on the HD if it's sent with the rest of the system.