Larry Sabato is already handicapping the 2006 Senate race:
The long and short of this analysis: Democrats have only a long-shot chance at Senate takeover, and they are short of opportunities to make it happen. Of course, if 2006 turns into a Democratic 1994, then even our mind-stretching list of upsets and perfect-D luck is a possibility. It's too early to tell, but we wouldn't bet on it, and we advise you not to bet on it either!
Read the whole thing, especially the part on gubernatorial races.