I'm going to guess the Intel PowerBooks (and probably Intel PowerMacs) will debut at WWDC in June 2006. Most of the people going to that conference use PowerBooks, it's kind of a natural place. MacWorld 2006 seems too early (with new iBooks and other stuff announced there, I don't think they'd want to dilute the message by introducing too many new CPU designs), and MacWorld 2007 definitely seems too late. WWDC is probably a date they can hold people off for, while giving them enough time to refine an entirely new design with the greater engineering demands of a PowerBook enclosure and higher-performance processing.