I have seen the link but never clicked on it. I suppose I assumed I would end up giving a book of mine away in return, but I am too possessive and don't want to give up a book! Also, I usually can find what I want at my favourite used bookstore where I can get credit for the books I bring in. I think its a great feature though and if I do have a book I want to get rid of I might use this tool.
Once a year I go through my library to see if there are books taking up space that I don't care for and that I don't think the used bookstore would take...they get dropped off the local firehall for the annual Calgary Book Drive & Sale for charity.