It isn't a safe pick I don't think. She will either help or hinder I think, possibly big time one way or the other. I am not particularly happy about it, as I thought it made sense to pick a more experienced vp, somebody that had actively run for the job, after all McCain will likely not be able to run again I don't think, if he wins now.
This could tell us something about McCain, which we probably already know, but I don't think he is comfortable with people around him that have previously opposed him. I hate to say that, but that is my impression.
Then I come back to the fact that usually after the focus is off the vp picks, people predominantly go back to voting for the candidate and tend to forget the vp, and once in office, the vps sometimes are nothing more than ceremonial positions. In McCain's case however, we needed something more than that.
There better not be any serious scandals. If there aren't, it may turn out okay.
These are my thoughts completely out of the blue, I have heard no analysis thus far.