PowerPage.org claims that PowerBooks aren't likely to be announced at Apple Expo. They also claim that it was not the Motorola Processor which is the bottleneck, but instead the assembly factory.
Previous reports from PowerPage claimed the 15" PowerBooks were ready and waiting, just waiting for stock to deplete... in May.
On the opposite end of the spectrum is LoopRumors.com -- with new PowerBooks "a certainty". LoopRumors recently was incorrect about details of the iMac update, claiming FW800 and case revisions would be accompanying yesterday's update.