I loved that thing.
I've somewhat-considered doing a "clone" with essentially the same functionality, but with modern components, and a real battery. I'd guess you could get 2-3 days out of it.
Other than that, I'm with you. Something just as rugged, with a somewhat denser display (80x24), very low power (msp430 comes in a couple of crazy low power variants and has plenty of oomf), bit more storage. Add maybe a PDF->text converter to the built in software and you're good to go.
Hrm, might have to start working on something. There are some crazy low-power ARMs around too, I'd have to do a bit of research.