It seems to me that McCain's choice of Sarah Palin is the reductio ad absurdum of VP politics and a clear sign that it's time to change this crazy system. Palin was obviously chosen in a campaign stunt that had everything to do with media impact and inflaming the Hillary vs. Obama storyline and absolutely nothing to do with governing. But even on the other side, the Obama campaign was considering the fairly inexperienced Tim Kaine for what were clearly electoral reasons, and Obama aides made it known that Joe Biden became a lock after Russia's invasion of Georgia colored the short-term conventional wisdom about what Obama "needed" in a running mate. (Not to draw equivalence here, because in the end Obama went with someone indisputably ready to be president.)
Clearly, narrow news-cycle politics and micro-electoral calculations have hopelessly warped the veep selection process. It really is absolutely crazy, and I'm with Matt Yglesias in calling for a new line-of-succession process that abolishes the office entirely.