Go2Mac has the scoop the upcoming Powerbook G4 (codename: Mercury).
There is no doubt that the new G4e processors will arrive in the new PowerBooks, but the main thing to remember is that they are subject to the same old supply constraints due to quality control.
They speculate about a Jan 2001 ship date, with current test models being used for "case design only" making it possibly stronger/lighter.
It's not clear whether these rumors preclude the release of G3 based PB's late this year, as hinted at by this ZDNet article
Update: Mac OS Rumors adds it's 2 cents with a report about the Pismo-B Powerbook due in September. They claim it to be based on 500-650mhz G3s from IBM.