MacOS Rumors updated with a new rumor on possible PowerBook and iBook upgrades later this year:
Apple's Titanium PowerBook is in for a change at Mac World New York. It will not be getting a case changing, but many other things will change
Upgrades include 1536x1024 rez, larger drives, batteries, and increased bus speed to 133MHz as well as processor bumps.
Their "source" also hints at faster G3 iBooks as well as 14" across the line.