I used various Handspring and Clié machines over the years and was eventually broken down by them because of their complexity - they are now trying to mimic a laptop in a tiny case - their instability - my Clié crashed about as much as my PC - and their dreadful battery life. Having to have two battery chargers, one at home and one at work, was ridiculous.
So I sold everything and went for the Zire. I realised I didn't actually use most of what those fancy handhelds offered, and the Zire supports what I actually do (read e-books, use the memo, date and address books, play chess, keep track of my current accounts) and no more. The battery life is tremendous - I'd say two weeks, which is a big improvement on four hours - and having an internal battery rather than being obliged to use AAA dry cells is great. And, if I lose or break my Zire, I can buy another one without too much pain.
I feel that, in many ways, the Zire recreates what handhelds were about before designers forgot that and they became ridiculously bloated.
Four stars, rather than five, because the lack of a backlight is a mistake although the screen has good contrast in natural or artificial light. The 16MHz chip is a bit slow, as scrolling through long e-books demonstrates, but the huge battery life makes up for it.