I have been a member of LibraryThing for a while. I started entering books read from January 2006. I love the ability to add tags, record the date the book was read. I am also a member of Shelfari. I believe I enjoy working more on Shelfari because it seems that I can do more in the program with my books. However, I could just feel this way because I have worked with the program more and have figured out how to network.
I introduced this site to my son's Humanities teacher and she had her students set up an account so they could begin entering the books they read over the summer. She has given them the power to share books with each other over the summer, but at the same time makes them accountable to her for their summer reading assignments.
I have been recording the books I have read since I was a child (not consistantly because I am constantly loosing the books in which I record the information). My mother has been recording her books since 1964. In fact this summer I have been entering her books into Shelfari so she can see the books she has read and allow her friends to see them too.