hi, this idea is not so new.
the gScreen Corp works on that, but manages the screens a little bit different, so nothing is out of balance :)

I agree with the rest of you but i want to add something,youcould have it to where the second screen is in the back not facing outward, then it can pivot and then flip around, with another screen in behind it the flip out in the same way, so that neither screen is facing out to where they could get scratched

I agree with chris. The weight of the 2nd screen would most likely add alot of off balance weight to the left side. Also. What sort of structural stress would mounting a 2nd screen onto the frame of the first create?

Or, make it 3 screens, so one slides left and one slides right, thus giving the notbook better balance.

This is Cool, I suggest to add a small support of pin on the left screen like that the laptop will not hang on the left side due to the weight of the screen.
:-)

Maybe the pivot instead of sliding it behind and becoming a dual screen make it swing so it becomes basically a back to back screen?