There are many advantages I can think of for using LibraryThing.
There is one thing I wish I had thought of before I started creating my catalog of books, though. Once I had a few hundred books in the catalog, I could no longer be sure whether a particular book I picked up was in the catalog yet, or not.
In retrospect, it seems obvious that I ought to have put some kind of tag or mark in each book as I entered it in the database, so I could see at a glance it was done. But not. So I have spent the past three days branding the books I've entered, checking many that weren't on a particular shelf - did I input that book, or not? I nearly wore out the search function for my catalog. Now I can be sure that all the books on nineteen shelves have been cataloged, and all the books on the remaining shelves have not yet been entered.
This has been a rather backwards way of organizing a library.
So, if anyone decides to catalog their books, here is an idea, for what it's worth - mark them as you enter them in the catalog, and you won't have to guess later, and search, to see if the work is done on them or not.