This LA Times article on the increasing political exhaustion within the evangelical community is potentially important stuff. The piece doesn't have much in the way of hard data, so it's unclear if its conclusions will hold as we barrel towards the general election, but it seems intuitively correct. Save for Huckabee, there's simply no one on the Republican side who can claim the natural affinity with the Religious Right that George W. Bush. Giuliani can pull Robertson's endorsement, of course, and Romney can line up his leaders, and Fred Thompson can profess his faith, but these elections are won on the margins, and that's where you'll see evangelical turnout drop-off. The segment of that voting population that's simply Republican will still show up, but the fraction who's voting evangelical won't prove so reliable.
Which is why I think you should expect Huckabee on the bottom of just about anyone's ticket, and assume that he'll be used to go on a tour of churches nationwide. He really does know how to speak the language. My hunch is that, as the Republicans grow more desperate, we're going to see a vice-presidential nominee who's little more than an official liaison to the religious community.