if you have an external mouse and keyboard plugged is as soon as your computer goes in clamshellmode (i think its called) everything shoudl works just as if you were usingit with the lid opened..
Can you do this with bluetooth input devices?
As for radiating heat, obviously and increase in surface area allows the machine to give off more heat. But, isnt the amount of heat coming from arears rather than the exhaust quite minimal?
I've never seen the need to close my lid when I'm using it.