up-side-down problems?

Are there any potential problems with running a macbook, while it is closed and positioned up-side-down?

I am currently using my macbook to power an HP 24" monitor, I keep the laptop under the desk (in a well ventilated area) and I like to keep it up-side down. It just seems to fit better that way, and also seems to shed it's heat more efficiently. I'm a little worried about this setup because it isn't how the macbook was designed to operate, is there any danger in running it in this manner?

The only danger I can think of is to the hard drive which are usually designed to be operated in either a horizontal or vertical position, not inverted. Surely you can place your MacBook upright and elevate it slightly to allow cooling?

Regards.