New PowerBooks use PowerPC 7457 [Updated]
The documents provide some detailed information on the hardware of the new PowerBooks.
There has been some debate about which processor is used in the new PowerBooks. With the increased L2 Cache (512k), it's clear that the computers use one of Motorola's newest processors: the 7447/7457. The only difference between these two processors is that the 7457 has the capability to support additional L3 Cache... which the PowerBooks do not incorporate at this time.
The documentation from Apple, however, links explicity to the MPC7457 information page at Motorola's site for further reference on the PowerBook's processor.
Update: Barefeats has posted benchmarks of the new 15" and 17" PowerBooks.