There may be an update before the end of the year. There is a rumor that IBM has a new G3 coming out that will have Altivec, but that won't be in this next revision. They already have a 1 and 1.1 GHz G3 that should be out by November. But we don't know when Apple will update the iBooks with them. According to the MacRumors
Buyers Guide, they were last updated on April 22nd, so it may be awhile before they get updated.
If you need it now, buy it now. Something better is always coming. There was a discussion about this awhile ago were I recommended someone buy an iBook, and someone who got a bad one was trying to tell everyone not to get one because of a bad logic board. Some people were hit with that problem, but Apple seems to have fixed it. I was playing with one at the store, I liked how rugged it felt, and was surprised at how fast it was.
I'm still leaning toward the 12" PB, which should be updated soon, but that iBook was really tough. And cool. For portability, I might just do what my Mom did and buy a used one from the studio my step-dad works at. Play around with it for awhile. I just wish it had 2 user upgradable RAM slots. With 128 MB it's usable, with 256 it's ok, and with 640 it's pretty responsive. Can you imagine how fast it would be with 1 GB+?
You know, without having to pay
$699. (edit: currently only available to the 17" PB)