After much consideration, I chose LibraryThing <http://www.librarything.com/> to investigate. Four hours later I am ready to start my post. This is not because it is difficult to use. It is quite simple to get started. I just got caught up in looking at the lists of other people who had books on common with my 5 item list and checking out the groups, especially "Librarians doing LibraryThing" (A lot more post on what librarians didn't like about their jobs, than what they did.)
The purpose of the site is to twofold. First it lets you easily catalog your book collection. It is even easier than finding the book on Amazon, because all the non-book ads aren't distracting you. Simply typing in the author, title, or ISBN starts a search process that brings a list you possible matches. Once you select the correct book, it, along with identifying material, is added to your list. You can choose to have information from Amazon, LoC, or one of over 70 other institutions. There are 5 different layouts for displaying your catalog. You have the options of rating, reviewing, and/or tagging your entries. The catalog is displayed in the reverse order of entry, but you can search by title, author, or tag.
The second purpose is social. Each book in your library has a note of how many other people using LibraryThing own the same book. If the person hasn't opted for privacy, you can follow links to his or her library and check out what other books are there. You can also set up groups for sharing about books. Some were huge, like the Harry Potter group, some were so specialized that they had only the person who started them. There has to be a way to use this feature for book groups for students, so that they can have discussions about the books they enjoy. There are some authors whose libraries are cataloged, so students may be able to see what their favorite authors like to read. Also, because the books are listed in the reverse order entered the latest entered (probably the most recently acquired/read) are on top, it's easy for friends to see what you've been reading lately.
I joined TeacherLibrarianNing. It was easy to do. There were some interesting postings. At this time I didn't feel that I had anything in particular to add to the conversation, but I am sure that as school begins I will.