I'm going to confess that I don't understand the great appeal of Library Thing. I have heard and read about how great it is and how the user communities are awesome, and (mostly) how horrible Shelfari is in comparison, and yet...I look at Library Thing and just think, "Meh."
I think the real barrier to my using LT is that pesky 200 book limit. Sure, I could shell out for unlimited space--it's not that expensive. But why would I do that when I can use another site and upload more books for free? Or start my own free blog, and blog about however many books I want to?
I think most people are drawn to the community--to having a space where they can talk about books, and who knows what else. This is probably where I lose interest. The message boards look sort of interesting, but I know I would never keep up with them. I don't have the time! I guess I'm lucky enough to get my fill of talking about books in the nonvirtual world.
I did set up my account--not sure how often I'll use it, though. I added the five books that are currently on my "To Be Read" shelf. http://www.librarything.com/catalog/reginalibris