I've had my 12" PowerBook for quite some time now (almost a year in a couple of weeks, I think...)
I can't help but say it's an excellent product. Mine has only suffered one drop, which didn't do much (a small dent, but it's hardly noticeable...) The actual build of the PowerBook is superb. There are no scratches on mine, and it's still almost indistinguishable from a brand new one. I had a 12" iBook before this PowerBook, and I can definitely say the PowerBook is a more solid machine.
Looking at the current timeline, I'd say don't expect new PowerBooks until April, or maybe May. March could happen, although I think it'd be very unlikely. I can almost guarantee you that new PowerBooks will have G5's in them. The iBooks might also get a speed bump sometime shortly after PowerBooks are updated.
If you want a solid product now that you want to last a long time, and don't think you'll need a G5 in the near future, then the PowerBook is probably the way to go. It's sleek, portable, compact, and it'll more than likely do everything you need it to do, with enough power for you to try something new with your PowerBook.
As far as battery life goes, I never have a problem with my PowerBook. I take it to class, and use quite frequently away from my room, and I never have power issues.
You also have to take into consideration that this generation of PowerBooks is possibly the best line of portables on the planet. They've gotten rave reviews from PC users who are jealous of their portability and style, and Linux users are eyeballing them because they can install linux on these fantastic portables. I get comments from people all the time about my PowerBook, on how small it is, how cool it looks, and how much they want one. The only bad thing anybody has ever said about it came from a friend of a friend who was using a plastic Dell notebook that was about twice as thick and heavy as my PowerBook. There was obviously a hint of jealousy in his snide remarks. Besides, the only thing he could say about it was that it only had a 1 button mouse, to which I quickly whipped out my portable mouse...
All in all, I think the PowerBook will last longer than an iBook, in terms of durability and power. The iBook is also a good machine, and if you're looking to upgrade to a G5 PowerBook later, then the iBook might be the way to go, so you don't pay as much now, but if you need a computer now, that you need to last for more than a year, then the 12" PowerBook is your machine.