My new 2004 R2000 is being put together at my LBS at this moment, and I can't wait to ride it home tonight.
I have no regrets of not waiting for the 2005 models, because I don't like the new color schemes, and only the really high end models come with my current wheel set (Ksyrium SL). The main differences are the new six13 frame, the shimano ultegra 10's, and the fizi'k arione seat.
Ultegra 10 isn't going to make it until early spring or so. So those are going to be 9 for a while. I think the six13 frame is a major difference, and aren't they going campagnolo, which means a different pair of wheels as well.