the circular scratches do indeed come from moving the console while it is on, I have kept mine horizontal the entire time ive had it and it does not "vibrate like a mofo".
it did however leave a crack in my initial copy of gears of war, and where it was at (along the center ring) im thinking it was caused because i was playing it in near freezing temperatures and the discs came out incredibly warm.. the sudden shift in temperature may have made the disc more brittle and prone to breakage(or i may just have a overactive brain and got a ****ty disc lol)
upon returning it, the guy that worked there said that it had happened to several other people with various 360 games.
since that day, my 360 has not put a scratch or a crack in any other games,