i've heard of a couple of experiments of this type, mostly in Europe (if memory serves, there were two schools in France, one in Nantes and one in Strasbourg --but i could be wrong-- and i think another in Germany maybe). However i don't remember hearing any follow-up stories once the programs were in place ; maybe they are waiting to do an evaluation at the end of a specific test period.
i did a quick search and came up with a few articles that might get you started :
Winthrop University
a Dutch school experiments with the iRex iLiad
a very old article about Carnegie Mellon experimenting with tablet pcs
and
a few threads about speculation and research into educational use.
i couldn't find the thread about the french school program but i'll keep looking and post here if i stumble across it.
i definitely think this is an excellent idea and education is an area where i could see reading devices being a huge advantage both for schools and for students ; but there are kinks to be worked out (and for younger students you might want to wait for the expected new devices with flexible and therefore far sturdier screens).