Only vote CP if you think the candidate can win. That means local office and such right now. State level may be a few years off.
Let's not blow the Hillary thing in '08.
Right now I would only vote CP if a) I preferred the candidate and the candidate could win, or b) I preferred the CP candidate, and the Republican is someone who is conservative enough that I would be ok with them as a second choice, and they are already guaranteed to win by a large margin (which never happens in California!)