I understand that user doesn't share credentials but usually, with facebook connect, the only method available to connect is where the site grabs a ton of information from facebook (name, email, profile interests, etc.) .. I'm not so sure I'd want to share it unless there's a reason to it..

e.g. Huffington Post asks for basic info (name, profile pic, gender, user id, list of friends and then some), access to my newsfeed, interests and likes, and my current city .. this is only to comment on a post .. it seems like overkill to me and as a result i wouldn't really use facebook connect in this instance.