I think Palin is probably going to have a big political career (just not VP!).

Mostly I don't think the VP picks add much to the ticket, but they can hurt. I don't think people change their vote to vote for a different presidential candidate based on the fact that they like the VP. I don't think Biden brings Obama very many votes, for example.

But VPs can hurt the ticket. I'm going to vote for Obama, but I think McCain is a decently respectable guy. Given a different Democratic candidate, I might have considered McCain, because he is a moderate and reformist and he himself is not an over-the-top social conservative. But I DO NOT like Sarah Palin's social conservative agenda. I would never consider voting for that whole ticket, especially given McCain's age and health. I don't think she will sway any on-the-fence voters for McCain, but she probably will help excite the unenthusistic social conservatives. And there is probably a good number of on-the-fence voters who will be repulsed by her.