Well if people have had a problem, why chance it? I’ve left my 360 on for days with no problems, and I talked to a few people in gamestop and EB games and they said they leave theirs on for weeks at a time in those barely vented enclosures with rare overheating problems. My fucking laptop overheats more in a day than everyone I know with a 360 has ever overheated.
I wouldn’t be worried.