I'd worry about design and build quality
I don't know if the latest iBooks have some of the design flaws fixed or not, but you might want to think about the longevity of your choice.
I bought a 600Mhz iBook about two and a half year ago and have used it almost every day, mainly for internet access, but also as a photo storage for digital pictures on holiday.
On the morning of going on holiday 4 weeks ago I started up the iBook to a blank screen, which ended up being the same fault a lot of iBook users find. There is a design flaw with the iBooks which can result in the screen display cable being broken/damaged, meaning your iBook may be perfectly fine, ie memory/disk/keyboard/screen etc, but because your cable linking the screen and system is broken/damaged your iBook becomes less than portable or even useless. Of course, you can send it back to Apple to fix, which they charge an arm and a leg for ( you would think they would be humble or at least generous about fixing a design fault in their product ) it, or you could try to fix it yourself, which is complex.
I've enjoyed my time with my iBook, but now it becomes an open laptop that I don't want to close in case it stops working altogether, the experience has soured slightly.
Just my two cents worth....