Well, this is the third thread in a row I've responded to under the "Buy now or later" category.
iPod, I really want one too, but don't currently have the money to get one, although I will definitely get one something next year, if not earlier.
I would definitely say MacWorld SF would be the place for an upgrade to happen, if it does.
I believe the iPods were last updated at MacWorld NY in July, when the 20 gig size, Windows iPods, and the solid state scroll wheel and remote, were all intro-ed, so I would say something is coming.
As for what that is, only a few people at Apple know that for sure. There are countless rumors and threads here about that very subject. Do a search for iPod in the forum, and you will most definitely finds all kinds of stuff.
As for which rumors are true, that is anyones guess. A size increase (maybe 30 gig) is probably the most likely, maybe Firewire 2 integration. Other possibilities include a color screen, the ability to play videos and display pictures and the ability for the iPod to work with all the iApps.
This is, of course, not to mention the numerous threads about new devices like the iPod, including the iPhone, the Apple PDA, and the Apple tablet.
What will happen, when it will happen, are both unknowns to everyone here. All we really know for sure is that something will happen, eventually. It always does.
-Natron