Apple offers the iBook G3 and the iBook G4 (both advertised today). Both with 30 GB HD, both with 800 MHz CPU clock, both with 12" screen... price difference is $300 !
There's also the difference of the optical drive (the G3 in that picture has a CD-ROM drive only) and the RAM configuration. (Although you'll want to replace the 128 MB block in the G4-model with a bigger one, anyway, so it'll be useless soon enough...)
...don't forget that the new iBooks use DDR RAM as well. There are quite a few differences besides the processor type if you look at the two models in depth.
If you just want a 12" Mac to carry with you, and you have a bigger one home, both do the same (let's put 512 MB RAM in each). I regret that the $800 is not on the main price list anymore.
They are both under full warrantee. This is from the "Special Deals" section where they sell refurb and closeout stuff, all under full warrantee, I just got my 17" iMac from there, who cares if it's refurbed, it still has the same warantee, plus someone went over it with a fine tooth comb before it was repackaged
On the original, I'd say the combo drive plus the bonus of having altivec is worth the $300. Not to mention the new one also is slot loading, which gives alot more rigidity to the case then the tray load in the G3 ibooks.