Does it help a political candidate to have celebrity endorsements? Do people really base their vote or use the endorsement of celebrities in deciding their vote? Does Obama gain votes with Oprah's endorsement? Did Wesley Clark (2004 election) lose votes because of Michael Moore's?
I'm not against people doing this, it is as good of reason as any to choose your vote. There seems to be much research done on celebrity product endorsement, but I see that as a signaling game because of the cost involved in hiring the celebrity. Celebrities seem to endorse candidates for free, demeaning the value of the signal. It seems to me that candidates are more likely to be hurt by a celebrity endorsement than aided by it, and since neither Obama nor Hilary as far as I could tell devoted resources to courting Richard Gere, they do not value it particularly high. They do seem to enjoy the ones they get, like when Huckabee got Chuck Norris.
I guess it would depend on what makes the "celebrity" a celebrity. I have been thinking entertainers, but Jon Stewart or Stephen Cobert are probably influential because their status is a function of watching politicians so closely.