Interesting results. Indeed, with a disc running and you switching the 360 position from horizontal to vertical or vice-versa, you hear a loud sound coming from within the DVD drive. There's a catch to this, though.
First off, I noticed that it only did it if I moved the 360 with quite a bit of force, meaning I moved it from vertical to horizontal quickly instead of carefully laying it down or standing it up.
Secondly, even though I did this approximately 10 times, with the obnoxious sound occuring every time, there's only 2 faint, round, even scratches on the outside of my disc. I restarted my xbox, and the disc still works fine.
So, I've come to the conclusion that the people with the scratched discs that don't work anymore simply were very, very careless, and damn near had to do it on purpose. I honestly can't see how having your disc scratched like that once, even twice, can ruin the whole disc.