Internet sites are reporting that the PowerBooks have all been end-of-life'd. This seems to be true, as there are now 3-5 and 7-10 day delays for shipping of the PowerBooks from the Apple Store, while the iBook, iMac, eMac, and PowerBook all have same day shipping. (This is good to see, since it means the 20" iMac G5 and the dual Power Mac G5 2.5 GHz are no longer in short supply.)
The end-of-life status of the PowerBook means that new PowerBooks will likely appear in early February. It is unclear what the specifications of the next PowerBooks will be, but it is widely expected that they will get G4 MC7447B speedbumps, to 1.5 GHz for the 12" and 1.67 GHz for the 15" and 17".
However, The Inquirer reports gaining access to a document that claims the HyperTransport Consortium has a design win with the PowerBook. If true, this would suggest the existence of a PowerBook G5, although it could just be a prototype which may appear later (or not at all).
It is also curious to see "apple_g5_powerbook" mentioned in the source code of the Apple PowerBook page. However, for all we know, it could just be a jokester web designer messing with us. :) The other reference to "sosumi" suggests that just might be the case. ;)
Apple has now changed the source to "apple_g4_powerbook".