Rumor-mill has it that apple has received or will be receiving soon shipments of mobile these new mobile penryn's. As such, they should have early batches and products off the line prior too or at the announcement date. Meaning they should reach stores before Macworld so we could see announcement sale turnarounds that accompanied the aluminum iMac. That is the hope at least. I also agree that there is a HUGE difference between a major hardware change (such as powerPC to intel chips that accompanied the switch in 2006) to a speed-bump/minor redesign that we should expect in 2008. Not to mention apple might already have cases under construction w/ hardware prepared sans that chips. Just things to consider before forecasting the worst case scenario.
-Josh