Kinda along the same lines... I always wondered why gas stoves are OK to use indoors. Think about it. Same basic concept as a furnace or dryer. But, the gas stoves don't have to be vented to the outdoors.
My buddy actually does use his dryer to heat the basement when we're playing pool/darts/drinking, but his is electric. The only downside we've found is that if we do that when clothes are actually drying, there is an incredible amount of moisture that gets spued about everything down there. It works better than one of those little baseboard heaters though.