Apple's PowerBook has seen the longest lead-times since revision... with the last PowerBook update released in April 2004.
Although initially predicting PowerBook updates for MWSF 2005, ThinkSecret recently revised their prediction to this Tuesday at the latest.
Despite speculation and rumors of PowerBook G5 updates, more realistic expectations predict G4 PowerBooks up to 1.5/1.67 GHz.
Recent unconfirmed hints, however, have noted that previous rumors of Dual-Core G4 processors making their way into the PowerBook may be true... with some expecting that the new PowerBooks will make use of the new dual-core G4 chips as early as this week.