Not that I think LibraryThing is bad. They all do a similar thing. What I like about Shelfari, is the ease of use and the fact that I can share my list, via the Bookshelf, on my blog. Which, as you can see, I've now added here.
I think something like this is especially important as I begin my career as a librarian. I think it's important to model to students that we are readers as well and this is one public way of sharing what we are reading. I also really like YA fiction, so I think it's great to share with my students that I'm reading some of the same books they are reading.
Obviously, I have a lot of work to do on my account, maybe that can be one of my winter break goals, to input as many books as I can remember that I've read.