There are many social networking sites on the expansive mess that is the internet, and some of them have a better reason for existence than others. Some of them are centered around some other useful purpose, while others, in the venerable words of somethingawful.com: are "Just a never-ending registration process that imports your address books and buddy lists and invites everyone you know into the registration process." Librarything.com is happily in the first group, a website that allows you to catalog and tag your library for easy reference, and also has social networking features that allow you to form groups with people who share similar interests or geographical locations. There is also a feature that compares libraries amongst users, and using some type of crazy algorithm determines who in the world has the same tastes in books as you do. The site is free for for the first 200 books, and then is either 10 dollars for a year, or 25 dollars for a lifetime membership. This is personally one of the few websites I have actually paid to be part of.
There are lots of things to like about the site, especially for a bibliophile. Each book has copious ways to examine it, including reading and writing reviews and tagging it. Some of the features are actually useful, like the ability to generate MLA and APA citations from any book in the library--which I find useful as a graduate student who sometimes has to add references to papers when I can not have the physical book handy. Others are mostly used for fun, such as the "suggester" which scans your library and finds books that you might also enjoy, and even more so, the "unsuggester", which after scanning my library, told me that "The Purpose Driven Church" and "Shopaholic Ties the Knot" are two books I would not like (something that I believe to be true). I have not had a chance to try out all the widgits and gadgets on the site as such, but the basic features keep me amused.
I haven't used the site much as a social networking site, although I do have some "friends" on there. (Most of whom actually came from here). I have joined some groups, but none of them actually seemed to have much interaction or be ways to meet people. Some sites seem to cause loyalty and group cohesion, with the members eventually making up a nickname for each other and constantly jetting around the world to meet up and get married. Although there is communication on the site, there is not, as far as I have seen, a great community. But, such a thing is not always necessary, especially because anything with books and more books is good enough for me.