you've heard of [friendster] right? if you haven't, friendster is considered a social network. we'll, if you've been using the latest version of [firefox] you might consider social bookmarks, at [del.icio.us]
on del.icio.us you can add, share, and find bookmarks. you can categorize your bookmarks, then add them to firefox as an rss feed so they are live bookmarks. the site looks like it is in pre-beta with some features such as alpha sorting not available. but hey why not give it a try or at least a look-see. you can see what bookmarks you have in common with others.