People were suspicious when John McCain claimed he hadn't decided on his running mate yet. But the Palin selection makes sense in that context.
A Pawlenty trial balloon went up... and got BB'd. A Romney trial balloon was met by an eerie silence. The Barack Speech went fabulously, and all of a sudden John McCain finds that the only card he has to play might not be enough to get people to stop talking about his speech.
So he called the only person that could possibly capture everyone's attention as strongly as Barack. Colin Powell demurred - he said he had to wash his hair today. Yes, all day. So McCain called Palin. That's why it doesn't seem like he's spent much time with Palin. That's why she seems a little un-vetted.