My LibraryThing catalog: http://www.librarything.com/catalog/marisaspar
As someone who collects books (OK, how many of us who work at libraries aren't guilty of this, to some extent), I found Library Thing very fun and helpful. I used it to catalog my collection of books by Patricia Beatty, although in the future I plan to use it to catalog my Lois Lenski and Marguerite de Angeli collections. (Hmm, I am beginning to think I have way too many collections!) I used ISBNs for the most part to add my books, and Library Thing did well, even finding the ISBNs for books from the 1970's. The only problem I ran into with this method was with a Scholastic edition of the title Bonanza Girl, (maybe Library Thing doesn't include Scholastic editions) which I ended up having to add by title. I also had to add by title some of the books in my collection that didn't have ISBNs listed in the book, but I was able to find the title with the correct publication year for each one. Being able to add tags for each title was very helpful; for each of the ones so far I gave it the tag "Beatty Collection," so that when I enter my other collections in the future I will be able to quickly identify the titles by which collection they belong to.
While taking the tour of Library Thing, I remember reading that you can access your catalog by cell phone while in a book store, an idea which I was very excited by. As any book collector knows, you need a list of what you already have in your collection while combing through the shelves of used book stores. I currently have lists of my collections in a physical "Book Diary" but I look forward to not having to lug this around once I get all my collections on Library Thing. Of course, I have to figure my cell phone out first!