If you ask me, which you haven't, 15 inches is the perfect size for a Powerbook's screen. It is big enough so that you don't have to squint, and small enough that it doesn't feel like you are toting around a desktop with you. Ken Mingis, of ComputerWorld, disagrees. He is a 17 inch man and says that the latest iteration of the Powerbook is the best yet.
The high res screen is the real killer feature of these Powerbooks, plus you get another hour or so of battery life. The big question is, should you have a G4 based Powerbook or wait for the Intel versions? Ken gives the same advice I do, if you can wait you should, but if you need a Powerbook now you can't go wrong with Apple's current offerings.