Laptops Aren't Meant To Be On Laps?

If you've been working with aptops a lot and you've been putting them on your laps, then you will have felt some heat. I once read that this heat can do some damage in a way I don't remember right now. Anyone heard of any such thing? Comments?

mine has fans under them, so if they're going to stay on me lap, i have to make sure i don't block the vents with ma lap. overall i don't keep them on me laps for too long, else ma legs would roast, don't know about the medical implications of lappies on laps.