I'm hoping this post wont spark a bunch of "360's hardware is faulty" responses, but I thought I'd post it anyway...
My 360 is on it's way to McAllen, Texas to get fixed. A few months ago every so often the 360 would think a game disk was a DVD and would play the DVD movie error if you were to put the game disk in a normal DVD player.
Normally restarting or re-inserting the game disk would stop it doing this, but then it started doing it all the time. So I called up Microsoft's support and off it goes.
I miss you!