I think it'll have a much higher "wow" factor than the iBook.
Compared to my Sony SRX, it's heavy at 4.6 lbs (Sony is 2.7 lbs; Doug's U3 is 1.8lbs) but just slightly larger. The Sony draws a lot of attention -- the PowerBook would draw even more. I think the integrated DVD/CD-RW drive (which I don't care about since I don't use such drives much) and metal case (which looks slick) add the extra weight.
A nice plus is the rated battery life is 5 hours, so it's probably pretty usable on batteries only (my SRX is rated at 6 tops, I seem to get around 4 -- but you can get a double size battery).
If I were going to get a Mac, I think the 12" PowerBook would be the one.
Tony