So listening to the Morning Edition web stream at work the other day, came across this:
Why Some Anti-Abortion Catholics Support Obama. It's a really thought-provoking article, and the audio stream is available, which I recommend, the article is verbatim but I like hearing the people quoted actually quoting their quotes.
For the tl;dr: Some Catholics believe Obama's polices would result in fewer abortions occuring than McCain's, and that single-issue voting ignores other social justice issues that Catholics and Christians in general are called by their faith to address.