Unfortunately, I have to agree with SICon here. Much as politics should take a back seat here in a perfect world, I need not remind anyone here that that world is not the Planet Earth. Quite frankly, this news is not good for the McCain/Palin ticket.
Neither the Left nor the Right are going to change their minds over this. SoCons are not going to suddenly withdraw their support for Palin (much to the shock of the Left who are gleefully expecting a mob brandishing pitchforks and torches) over a mistake so many teenage girls (generally very silly creatures by nature - teenage boys are stupid) make even when they hale from the best of homes.
The Left, who are not particularly enamored of child birth anyway, are going to be enraged since there would be no abortion as a result of this, but since Palin drawing breath already has them foaming at the mouth, what difference does it make?
The real problem is that great electorally significant plurality of voters, the "Muddle" i.e. the "swing vote" - who tend to decide elections. For people who vote based on memes, impressions, press coverage and whatever passes for conventional "wisdom", the "hypocrisy" meme could all too easily strike home.
Let us not deceive ourselves, this complicates our task in November somewhat, to say the least. The Press is going to be the number one enemy here, not the Democrats, I think - allowing the Democrats enough space for plausible deniability.
In other words, they'll do their subtle and not-so-subtle utmost to link Palin's fitness for the Vice Presidency to her daughter's mistake and heavily hint that the Palin family is dysfunctional. And chances are it would work.
The McCain campaign, I hope, has already foreseen this and planned for it. I don't see much of any way to turn this into a positive, but I've been surprised before by this campaign - with this as the latest unforeseen twist in the story of Election 2008.
You have my prayers, Bristol Palin.