With the PMA show around the corner in late January 2008, and the rumor mills in full churn about upcoming announcements, you might want to take all of this into consideration if you're in the market for a new Canon DSLR.
Canon shooters are safe in the middle of the line up. The 40D was released in the Fall, and it is as solid and highly reviewed as they come. If you're looking to upgrade from a 10D, 20D, or even 30D, you're safe to buy now. Nothing new is going to happen in January for those mid-line bodies.
But if you're in the market to upgrade a Digital Rebel or EOS 5D, I'd hang on a few weeks. It's very likely that announcements for new versions of those cameras will come in mid-January 2008. There's no guarantee of course, but if you have the luxury of time, why not wait and see?