Definitely worth a look. Props to Dennis for the heads-up on the iBook monitor-spanning hack.

Feature
PowerBook iBook Notes
Processor
1.5-GHz G4 1.2-GHz G4 300-MHz difference
System bus
167-MHz 133-MHz 34-MHz difference
RAM
512 MB 256 MB 256 MB difference; both will need added RAM
RAM limit
2 GB 1.25 GB 750 MB difference; not a significant factor
Hard drive
80 GB @ 5400 rpm 60 GB @ 4200 rpm 20 GB and big speed advantage
SuperDrive
4x 4x equal
Display
15.2" 14.1" 1.1" advantage to PowerBook
Resolution
1280 x 854 1024 x 768
Monitor spanning
Yes Yes, with hack
Graphics support
128 VRAM (4x AGP) 32 MB VRAM (4x AGP) PowerBook video card is significantly faster and more capable
Video outs
ADC, DVI, VGA, S-video, composite VGA, S-video, composite Some require adapters
Modem
56k V.92 56k V.92
Ethernet
10/100/1000BASE-T 10/100BASE-T Gigabit ethernet is still relatively uncommon
Airport Extreme
Yes Yes
Bluetooth
Yes Yes
USB
2 USB 2.0 ports 2 USB 2.0 ports
FireWire 400
1 port 1 port
FireWire 800
1 port none Not a major deal today; might in the future
Audio in
Microphone, line-in Microphone only Work around is to use a USB mic
Audio out
Speakers, headphone jack Speakers, headphone jack
Battery life
4.5 hours 6 hours Big win here for the iBook
Weight
5.7 lbs 5.9 lbs.
Extras
Backlit keyboard, PC card slot Card slot is potentially useful
Cost
$2389 $1624 Ed price of computers as modified; $765 more for PowerBook

Comments/suggestions welcome!