My mom was one of these mythical Catholic liberals. She got as far as postulate in the convent before decided she was tired of being treated like dirt as a nun, so she ran off and joined the Army instead. (Where she met my dad, so I'm glad.)
She was a labor Democrat from Detroit, and while she was a superficially devout Catholic, she also believed in UFOs and Roswell aliens. I think the only reason she went to church at all was, as Smash said, for the sense of community.
(I'm a lapsed Catholic. I left when I turned 18 and discovered I didn't believe in the religion at all, I just thought the music was pretty. Doh!)
Also, one of the last things I heard my mom say was that she hated the new Pope and didn't think he was really the person ordained by God. HERESY!