This is definitely a machine for early adopters with burning wallets!!
It may well be a big performance improvement (if you believe Apple's claims...) but in rushing this machine out ahead of schedule they seem to have binned some useful features and others have gone backwards. At a guess I'd say this is to keep the price of the machine down, though it's still pricey.
These are the main backward steps I can see compared to the PowerBook G4:
Slower SuperDrive lacking dual-layer DVD burning support.
No FireWire 800.
No PC card slot (ExpressCard/34 isn't widely supported yet).
No internal modem (not everywhere has broadband yet).
No sudden motion sensor (not mentioned in tech specs).
No S-Video output (not all video equipment has a DVI input).
Lower resolution display (nearly 9% less pixels).
Clumsy name!
I bought an October revision PowerBook G4 1.67GHz and don't regret not hanging on for these new machines. The G4 is more than fast enough for what I need and the removed/downgraded features are things I'd miss. I'll be waiting until these Intel Macs are much more mature and fuller-featured before I think about upgrading again.