The folks over at Ars Technica are already on site to prepare for the 2008 Mac World San Francisco expo which starts next tuesday (we'll try and cover the Keynote live). And they have posted a couple of shots showing the first teaser banners that Apple has started hanging at the Moscone Center:

<div align="center"></div>

It reads "2008 There's something in the air"... as always, these teasers are done to effectively tease us, and it's difficult to know what that one means, but it smells like "wireless", so maybe we'll have some sort of new Airport-related product, or a 3G iPhone, or some form of wireless streaming of media.
My personal interpretation is that Apple will release an hoverMac: a Mac that will levitate above your desk using some sort of gravity distortion field ;-)

Well, we'll see and I'll try and post some more shots as soon as I arrive in San Francisco monday afternoon.

Stay tuned.

My bet is a tablet mac.

In the US it is widely assumed that the Big Thing ("something in the air") will be a new and improved Apple TV + announcement of a library of movies by several major studios available for rental downloads. It would seem that the new generation of MacPros was announced prior to the Keynote address because Apple didn't want to divert any attention from this one thing. (I'm sure that sometime in 2008 we'll see a new generation of iPhones, but maybe sometime later in the year is more likely).