Yeah, I’ve had a LibraryThing account for a while too. I use it (in true-to-self fashion) as a tool for displaying/highlighting recommended books on a website somewhere else. I’ve never explored the social web part, mostly because I have seven gazillion other ways of finding out about books. “Books-a-plenty, books galore!” is my life.
I do like that Groups area, though. That’s pretty neat, and I could see using and perhaps even participating in a group of interest. Tags are handy, but they are also pretty scattershot; mine are mostly relevant to me, not necessarily to you. The Groups have additional criteria, so the likelihood of finding relevant & quality books seems to be a lot higher — Asian Fiction & Non-Fiction in a group won’t include Japanese manga (probably) but tags Japan & fiction might. The Read YA Books group discusses a different young adult title every month. With a group of dedicated readers, a library could have reading discussions over the summer this way, or students could track their summer reading — including the progress monitor is a cool visual. A group of far-flung friends could share & discuss favorite books in a LibraryThing group.
Aside from the blog widget that I like so much, most of the uses I can envision right now for using LibraryThing in my work/life are pretty much re-inventing the wheel, and not very effectvely at that. I’ve heard of small libraries using LibraryThing to catalog their collections because they don’t have an automated system — awesome, but not useful for us. A printed summer reading guide is a lot easier and more useful than inputting titles online. And I don’t own enough books to care about cataloging them at home — I get all my reading from a library!!!