This may be Apple's last time at Macworld, but don't expect the company to go out with a whimper. They've gone to the trouble to be there one last time, and they'll be wanting some marketing mileage in return.
The rumor mill seems nearly certain that both the iMac and the Mac mini will see updates at MWSF-09. There's also speculation about a revised Time Capsule with expanded functionality. Some think Apple TV will become a Mac application, given that all new Macs will have video hardware adequate to the task, when combined with signal/pinout converters in dongles. And many anticipate the demonstration of a nearly complete Snow Leopard.
I have a hunch there's something else, something that's completely escaped the attention of the rumor mill, and that the presentation of this something is the main reason Phil Schiller will be acting as emcee for the keynote. But that's all I'm going to say about it, because I don't want to spoil the surprise in the off-chance that I'm right about what that something might be.
So, rather than talk about that, let me just say that those in attendance at the keynote shouldn't be too surprised if Steve Jobs shows up as a Max Headroom-like character, not only on the main screen but also on their laptops and phones, providing a humorous counterpoint to Schiller's uncharacteristically deadpan delivery. Something equally unexpected is likely to happen. ;-)