Here's an article suggesting Barack Obama is losing the votes of moderate evangelicals who are pro-life and moderate on other issues. It points to Obama poor performance at the Saddleback presidential forum, publicizing of his very pro-abortion record while a state Senator, running pro-abortion ads, and support for forcing faith-based organizations participating in government programs hire people who don't share their faith, and nomination of a strong, prolife VP candidate Palin.
I suspect Obama will start having problems across the board as his very liberal positions on other issues get greater public attention.
While Obama is still slightly ahead in the polls at this date, the momentum is clearly on McCain's side. While there's disapproval of Bush, Obama's proposals are nothing new - higher taxes, more government and radical social policies. That's really a continuance of the long term status quo.