4Marks.com is a Catholic social site with a very friendly community, and almost a professional veneer (though it is not like LinkedIn, which is almost exclusively professional). Indeed, I have found 4Marks an excellent place to interact with Catholic authors and musical artists whose works I might sell through From the Abbey Catholic Books & Media.
The focus of 4Marks seems two-fold. First, it does a great job pooling Catholics together who have common interests. 4Marks is experimenting with social groups (a construct also found on John 654). You can find a group for almost any special interest: Catholic books, Lay Dominicans, Pro-Life, Canadian Catholics, specific diocesan groups, Catholic writers, Catholic musicians, Catholic businesses, etc. Secondly, 4Marks really focuses on user-generated content. It offers users the ability to create and/or post blogs, podcasts, articles, forums, pictures, videos, public calendars, and polls. Users can also take a temperaments quiz and post their personality type on their “folio” pages, and participate in trivia quizzes. The result is a great pool of user-generated content, mixed with professional content posted by 4Marks.
I have been involved in a number of conversations on 4Marks. I have found that these conversations are much friendlier than on Catholic Answers Forums. However, they are also much slower. 4Marks would not be my first place to turn for immediate answers to questions. However, I would be much more likely (if time allowed) to make 4Marks a daily community than I would Catholic Answers.