I was actually going to make a thread about this, tho it's not the biggest of deals, but since this thread talks about disk scratching it'll fit in here just fine. Apparently someone took MS to court over this (and wanted some ungodly sum ($50,000) they don't deserve for this particular problem), and apparently a MS suit admitted to knowing about this problem before the 360 ever shipped.
I'll post the link to this at the end, but from what I read, it seems that it scratches if you move the 360 while the disk is spinning. So if you have it verticle and move it horizontal mid game, you could scratch it. MS not only knew this, but had 3 plans to fix it which they never implemented. One of which would only have cost them 50 cents per machine.
I doubt this becomes a big case or anything, but just thought I'd pass on that info. This article I'm linking was posted only 2 days ago so it's still pretty new.
http://videogames.yahoo.com/feature/microsoft-faces-new-xbox-360-reliability-accusations/1274293