Eh, I still doubt G5 PowerBooks are gonna be here this year. Too many reports of the G5 chip fab process not being small/heat efficient enough for notebook use. We can hope for another "One last thing..." from Steve, but I really doubt it.
I'm expecting a re-cap of G5 speed bumps/redesign (a la AppleInsider's photos, and no 3.0GHz), AirPort Express intro and demonstration for about 30 minutes of the keynote, and an overview of iTunes 4.6. A color iPod, perhaps with WiFi built in for compatibility with AirPort Express. The PowerBooks were just updated not two months ago, so I'm gonna say no PowerBook updates.
If you think realistically, then the keynotes these last few years have been pretty predictable. Steve hasn't proven anyone drastically wrong recently or released anything groundbreaking that we didn't already expect.