On June 3rd, a MacPolls.com poll revealed that 32.89% of readers were waiting primarily for PowerBook updates. Unfortunately, those readers are still waiting... nearly 9 weeks later.
Previous Updates
15" PowerBooks were last updated in November 2002, with the introduction 1GHz machines with the Superdrive at the top end.
12" and 17" PowerBooks were introduced with little warning at Macworld San Francisco in January 2003. Almost immediately, rumors of a 15" PowerBook updates emerged.
(Timeline available at BuyersGuide.MacRumors.com)
Previous Rumors
Numerous sites have suggested 15" PowerBook revisions over the past 7 months: MacWhispers (Feb), SpyMac (Feb), Kodawarisan (March), PowerPage.org (April), MacBidouile (May 14), RailHeadDesign (May), Kodawarisan ( June), MacWhispers (June), DigiTimes (June).
In June, Apple dropped 12" and 15" PowerBook prices, which (in retrospect) may have hinted that PowerBook updates were not imminent.
Rumors peaked pre-WWDC with one site claiming 970 PowerBooks were arriving. No PowerBooks arrived, and one Apple executive finally hinted that PowerBooks would not see the G5 processor "anytime soon".
So When?
Speculation and rumors have placed the Motorola MPC7457 PowerPC Processor into the next PowerBook revisions.
The processor is expected to ship in Q4 2003, and reports from Appleinsider claiming that the PowerBooks have been delayed due to the inability for Motorola to produce enough of these updated processors.
Even with a Q4 ship date expectation, the most recent rumors from MacBidouille (of uncertain reliability) suggest August 18-19th as possible dates for product introductions... however, no other reliable sources have confirmed this timeframe. Beyond these dates, the next major consumer event from Apple is Apple Expo on September 16, 2003 in Paris, France.