Wait, so how is this different from Goodreads?
From what I can see, Goodreads looks like a social network for book lovers. LibraryThing offers more for book owners who wish to electronically catalog their collection and tag them with specific terms, so as it is easier to find books for a certain topic.
Take my Tags page for example (http://www.librarything.com/tags/Rhythmroo
): That's a fraction of the amount of tags I'm going to be adding to this for cataloging my books. I don't have that option in Goodreads, only putting books in my collection and telling everyone that I read it, in the process of reading it, rated it, and/or reviewed it.
I probably would recommend Goodreads for people who love books and want to connect with other book lovers, but would not recommend it for people who are trying to archive/catalog their collection by their own criteria--then I would recommend Librarything.com.
I hope this answers your question. :)