I am quite interested in social networks as they allow you to get in contact with people with similar interests.
I found some time ago a social bookmarking site called delicious.com that allows you to have all you public bookmarks tagged. I liked to find similar users to me but the site had no option for that and I found Find Similar Users on del.icio.us but it had some problems like excessive memory usage, no continue and the need to provide user and password to access the data. So I developed a similar Java program without those problems called Social Bookmarks Friend Finder (for delicious.com). It is coded in Java, using the embedded H2 database by default (being able to use most compatible JDBC databases). Please try it if you want and report any issues. I would like to hear if it was useful to you!