Guys, when trying to see into the future, get rid of what you want and try to predict what is realistic. I SOOOO want a G5 Powerbook - but it ain't going to happen anytime soon - or else Steve would have announced it at WWDC...
The power consumption of these chips is far more than the marketing document would have you believe. That is the reason for the overdesign of the case, the cooling system and the G5 heatsinks. It's not just for noise issues - the FP iMac and Cube are also very quiet but do not have such overdesigned cooling systems.
Quote:
As stated by Greg Joswiak
Our partnership with Motorola is not going away, G4s are in every other part of our product line. As you can see, [the G5] is not going in a PowerBook anytime soon. Motorola remains very important to us, but IBM is the one that can take us to the next level.
Besides taking the statement at face value, it seems that the "As you can see..." comment is referring to the heat issue...
Take a look at this chart. It extrapolates where the 1 GHz 970 would be based on the EETimes numbers...

As this shows, best case at 1GHz would be around 30W and the power consumption could be more.