As stated above, the only thing that is true is that there WILL be an update to the PB and that logic would dictate fairly soon as it has been over 6 months since the last one, there is a trade in program ending this week, and there were just price drops on refurbs.
Having said that, I wouldn't expect the G5 to get into the PB anytime soon. Some people are extremely optimistic that it will, but there are heat issues, not so much with the CPU now but with the remainder of the architecture. There is also the comment from an Apple executive that the G4 will be around for sometime to come, and Jobs even said we would like to see a G5 PB by the end of the year (2004). In short, the only people saying the G5 will be in the PB soon are the ones guessing. Apple hasn't even alluded to this fact.
Transitions take time sometimes. When the G4 first came out in the desktop lineup it took 18 months to come out in the laptops.
My personal opinion, there will be another G4 updated PB soon within the next month or two (MY OPINION), and a G5 PB after that (Fall, early 2005?).
Cheers!
Ian