I read all the time on my DSi using DSlibris, an open source DS app available on Sourceforge. The main problem is one of resolution. It's nice that the new DS has a larger display, but it's still at the same resolution of 256x192 per screen!

B

I've done some reading on the DS Lite, as part of the brain age game. It works well for me, and the new screen will be bigger so it seems like a winner.

Bill - the DS folds in half, and each side has it's own display; in that respect, it offers more of a 'book-like' experience than any competetor. Perhapse you could try it and then judge. :)

It have 2x4.2" screens, but I bet reading in such screens are probably awful. They are too narrow. And the experience is completely different than a real book reading. A feature that is a must to a succesful e-reader.
A single 10~12" screen would be the perfect reader. Not too small, not too big... Reading in 2 small screens is far from what I consider a pleasant idea.