I have never understood the great flurry of interest in the selection of a Presidential running mate. This is a person who gets a few photo ops with the Candidate on the podium at the convention, makes a few speeches during the campaign, and gets one debate with the VP candidate from the other side. They are supposed to bring votes to the top guy in a region or state where they are weak. Then, when elected, they sit in their office for four years doing nothing, attending state funerals when necessary, and collecting a paycheck. Why this is deemed important is beyond me.
This election (assuming that McCain is the nominee of the Republicans), the VP nomination takes on some level of meaning beyond just a few uncommitted votes in the deep south.
John McCain has been clashing with conservatives for many years, and has missed few opportunities to poke them in the eye (as examples, I give you his "agents of intolerance" quote, McCain-Feingold, McCain-Kennedy, and the "Gang of 14"). But now, he needs us. He needs us to come out and vote for him on election day in order to offset the Obama Zombies. His rhetoric has been changing somewhat toward us, and he has apparently seen the light on solutions to the illegal immigrant problem. Still, most real conservatives don't trust him any farther than they can throw him.
This is where his choice for VP becomes important. There are rumors of Giuliani or Romney, neither of whom are conservative, and neither of whom inspire much of a following (all we have to do is look at their primary performances to see that). If McCain picks anyone like these two, or someone who is a "moderate", there won't be much of a chance for real conservatives to embrace McCain.
However, if he selects someone who is a known, committed, real conservative, it can be seen as an indicator that he understands at some level that it is conservatives who are going to win this election for him, and not crossover democrats and liberal republicans.
It would remain to be seen if this epiphany would last beyond Inauguration Day, however. There's that trust thing again.