The endorsements that matter to me are Parents, close friends in the political world, and those I know who personally know candidates. My biggest factor are the records of the candidates themselves in making my own decision.
As for not voting for someone, I look at the Brady Campaign, UAW, MEA, Planned Parenthood, and NARAL.
As far as celebrities, I don't care who they back. I've met many famous people. They range from good people to jerks like everybody else.
I agree with you about endorsements. I am not impressed like the Left is with having celebrity endorsements of my candidates. However, since it takes a considerable amount of courage for celebrities to break away from the pack to endorse Republicans(and most likely be attacked by their peers and given fewer roles,) I do respect them and appreciate them for their decision to take a stand. Meanwhile it takes absolutely no courage for the bevy of airhead actresses and Hollywood elite to endorse Democrats. "Everybody" is doing it.