Well it turns out there's already something like that, called the "EnTourage eDGe."
Stupid name aside, it looks really awesome. In theory. In practice the current implementation has a few problems. I'd be really tempted to get one if the came out with a version that met at least some of the following criteria:
Full Android 2.2, complete with access to the Android App store
Multi-touch (on both screens)
Ability to use either touchscreen as a virtual keyboard for the other screen (this seems like such a no-brainer that maybe it already does that, but i haven't seen specific mention of it anywhere.)
Ability to use either touchscreen as a pointer device for the other screen, either in laptop configuration or on the reverse side.
Less than $500
Apparently some people think it's too heavy at 3 lbs, but i'm not sure if i'd actually mind that. Still, i certainly wouldn't complain if they managed to make it lighter.
On the other hand, OLPC is planning on making a cheap tablet with their XO-3 model. (Sadly, the XO-2 model, which was going to be something vaguely like the eDGe, was canceled.) They claim they're going to get the price down to $100. I don't really believe that, but if they could get it down to $200 that would make deciding to go with a $500 eDGe a lot harder. Of course as far as their organization's goal go i'm really not convinced that a tablet computer is a better learning tool for kids than a laptop/netbook computer.