My two cents on this is that Palin did enough to make the people already voting for the McCain/Palin ticket feel better about their choice. She didn't make any huge mistakes and she stuck to the script well. She certainly came off better here than in the interviews, although I don't think the format of the debate allowed her to be pressed hard enough, oddly enough.
However, Joe Biden very clearly won that debate. He was much more in tune with the public on issues from the economy, health care, international politics, etc. It wasn't really a fair fight, so that much at least went as expected. So while Palin comforted the base to some degree, I don't think any undecideds are going to break for McCain/Palin as a result of her better-than-expected performance. The early poll returns, at least from what CNN reported, have Joe Biden winning, as well.