True, but in this case all the information I have suggests that the G5 PowerBook won't be available until at least Mid-2005, though I suspect it may be as late as Jan-2006. The info I have is that Apple and IBM are trialling a handful of different processor options at the moment and are getting some very promising results, but its still not ready to be tested in prototype models.
These are likely to be running about a 1.4 to 1.8ghz G5 so its not really worth waiting 6-10 months for the launch, then another 6-8 weeks for one to ship, unless you're really going to get some benefit from the G5.
The current G4 PowerBooks use a very optimised, mature and reliable processor and will make light work of some quite hefty tasks, so I'd just recommend going ahead and getting yourself the current model. You won't be disappointed!