I have never heard of LibraryThing but was recently introduced to Shelfari which is very similar. They both have the same concept which gears towards book lovers. I like Library Thing although I would prefer Shelfari instead. When I was exploring LibraryThing, I had to think of the titles of books I wanted to add which was a little difficult. I like that Shelfari allows you to choose from books that are categorized for you according to most popular, most comments, and best reviews. Looking at the book covers allows me to choose books that might be of interest. I did like that LibraryThing has a list of topics to read from as well as blogs which were on the right side.
It think both sites would be great for students to have book discussions with other schools. I have lots of friends who are third grade teachers in other districts and I think it would be fun if we could set up a group discussion for our students to participate in. I know they would enjoy it knowing that students from other districts are reading their comments.