A quick comparison / review between the 12 inch portables that Apple has available now. The Powerbook is more expensive by about 400 pounds. This is based on approximately equivalent specs from the Apple store.
Powerbook G4 12 inch 1,497.98 pounds (Amazon.com)
1GHz PowerPC G4
512MB DDR266 SDRAM - 2 SO-DIMMs
60GB Ultra ATA drive (4200rpm)
DVD/CD-RW
12.1-inch TFT display
NVIDIA GeForce FX GO 5200 - 32MB DDR
AirPort Extreme Card
iBook G4 12 inch 1,063.00 pounds (Amazon.com)
800MHz PowerPC G4
384MB DDR266 SDRAM - 2 SO-DIMMs
60GB Ultra ATA drive
DVD/CD-RW
12-inch TFT display
ATI Mobility Radeon 9200 32MB video memory
Bluetooth Module
AirPort Extreme Card
So for your 400 quid you get a faster CPU and more opportunities for expansion. If you have no need for driving double monitors, then I'd get the iBook, as it seems a steal, Apple Store iBook link.
The PowerBook G4 also has a faster bus and memory, but how much you'd notice that I'm not sure. Also, Bluetooth is built in on the PowerBook; if you don't have it built in at BTO time on the iBook, you're stuck without it.
Generally, though, yes, the 12" PowerBook looks pretty weak against the 12" iBook. (I don't think that's the case with the 15" PowerBook, especially once you've moved up to the SuperDrive/ lit keyboard/ AirPort enabled model; the