McCain needs to get people who can be persuaded to do so to take a second look at him. (If this doesn't apply to you, that's fine. I suspect that McCain could have picked the deity of your choice as his running mate with a divinely-backed promise of Peace on Earth and he still wouldn't be your preferred candidate. :) ) Palin provides that in a way that none of the supposed front-running choices could have. Whether it will make a difference remains to be seen.
And I am absolutely thrilled to have someone on board the Republican ticket who has made her reputation by going in, kicking butt, and taking names in her efforts to rid her own party of corruption. If it were possible to say the same about Senator Obama, I'd be much less worried about him than I am. (Yes, I know about the investigation into Palin. It appears to be a non-event. Certainly McCain knew about it and picked her anyway.)
That is change that I can believe in.
I wish we had such Republicans in Illinois.