Guy I know on another site had this happen to him. He is a MS/XB fan and would not make this up or lie. But here it is...
http://www.pocketpiglets.com/private/toasted.jpg
http://www.pocketpiglets.com/private/toasted2.jpg
Power to the 360 was off.
Room 74 degrees.
Well vented.
Only played a few times.
Didnt make a smell or sound, just burned up.