I have both a Nokia N810 and a PRS-505. Love the N810 when I'm traveling and don't want to bring a laptop. For the daily commute, though, I do most of the reading on the 505. The N810's battery is fine (a couple of days on a charge)... but I can't remember the last time I actually had to think about charging the 505 --- plugging it into the USB port for a few minutes in the morning to pick up my copy of BBC from Feedbooks has it topped off for the day!
Can't comment on the JetBook --- but the Nokia 800 and 810 are both good devices, and if you shop around, you can get a good deal on one.