I think that for those using PowerBooks, the ideal time to upgrade to a MacBook or MPB will be after the next refresh. The current MBP processor uses 34W, and the new Montevina refresh will use about 29W. The next refresh after that is going to be Nehalem in Q2 2009, which is going to be use between 35-45W, probably at least 40 for the version that will go into the MPB. So the new Montevina chips seem to be striking the best balance between speed and battery life. The 22nm Sandy Bridge refresh will fix the power consumption problems, but that doesn't come out until 2011. Since realistically no one still using a PowerBook will wait until 2011 to buy a new one, it seems like the optimal time to upgrade is going to be in late August or whenever the new ones come out.