Hmm...

Yesterday I played Gears of War for about 6 hours straight - Multiplayer Host. No air con. Nothing happened There were a few occasions of Guide lag (Where the Guide just froze. Took about 15 - 30 seconds or more to un-freeze) when I was trying to invite people but other than that everything seemed to be fine.

On a side note, I put my power brick on a shoe box for extra ventilation. I dunno if that would help or not but I've been doing this ever since I got my 360