The absolutely only thing I miss about treebooks (I like the word) is the better contrast. The contrast ratio of actual e-ink screens must improve. With good light, it's fine. But if you read at night, in bed, with a not so bright light, than you feel the diference. The paper is still superior in this regard.
I hope the next generation of e-ink devices come fast! (2010 will be the year, it seems)
I haven't read a treebook for about 16 months now! (seems like I am in some kind of therapy!

)
Regards