To senne's questions:
a) The PowerPC 7457 has a larger (512K) level 2 cache and is, overall, a more evolved chip than the previously used chips (7410, 7451, 7455).
b) The graphics card certainly has an impact. Mostly for the games, of course, but also for GUI tasks.
c) The bus is faster, which always plays a big role.
I'm glad that the new PBs are that much faster. Sure, they're not what I was hoping for, but they're what I've expected.
Sadly, this means that the gap between the desktop and mobile Macs is getting bigger and bigger. Steve Jobs himself is talking about how important notebooks are to Apple, so they should put all their money and energy into getting a PowerBook G5 ready for MWSF 2004 in January. And if that isn't possible, I hope that Motorola once can deliver what they promise and bring us a PowerPC 7457-RM at 1.833 GHz. The PowerBooks deserve this, and the iBooks could sure make use of the 1.25 GHz PowerPC 7457. Alas, we _do_ know a bit about Motorola, and maybe it's better if Apple goes G5 (90 nm) for the PowerBooks and uses the ever faster G3s from IBM for the iBooks.