According to an anonymous report...
In light of the ongoing difficulties in incorporating desktop-class processors (such as the PowerPC 970) into the PowerBook, Apple and IBM have laid the foundation for an architectural revamp of the PowerPC to produce an ultra low power 64-bit mobile processor.
According to this report, the upcoming mobile PowerPC will be part of a 300 series of processors from IBM. This new mobile processor is not due to debut until 2005.