I'm no CPU specialist, but the new front side bus and cache is part of the new architechture of the 970 CPU.
Perhaps you have noticed Gary, the IBM chip doesn't have a L3 cache at all (while the G4 had up to 2 MB).
The large cache of the G4 was Motorola's last effort to squeeze the last bit of power out of the G4 chip.
The big cache of the G4 was often critizied. But I can't tell you why or why it was so bad.
As for the design, I am not quite sure if I like the front.
And I definitely don't like the fact that it only has one optical drive.
Nonetheless, I am going to order one.