I don't know about anyone else, but 80% of what I use my PDA for is reading e-books. It's so much more convenient than paper! But even I have to admit that LCD screens are sometimes not as nice as they could be.
Which is why I've always been interested in the Phillips E Ink technology. But recently Sony announced that they are actually going to release a device with an E Ink screen, in "late April". Yes, this year!
Check it out:
http://eink.com/news/releases/pr70.html
The screen is absolutely beautiful:
http://eink.com/news/images/SONY_Reader_1000EP.jpg
I personally would love the higher DPI on a PDA, and don't mind the lack of color. It sounds like the battery life would be very good too.
eeksock