There is no cost to sign up and use the website. But you will have to pay for the cost of shipping your books to the receivers. I still think this is a fair trade off seeing as you also get books from others free of charge.
There are ways to leave feedback on a sender just like you can for eBay or Amazon, to help others when they are looking for a reliable sender and a good book. While we are on the topic of Amazon, this is how BookMooch runs. If you can't find a particular book your looking for or you just plainly want a new book in good condition if you follow the link to the Amazon page for that particular book and order it BookMooch receives a potion of the goods.
It's an international website so you can find books from other countries like England or Germany. If you ship anything internationally you gain 3 points rather than 1. To receive a book internationally it cost 2 points.
I have signed up to use the website and am very eager to get started on using it. So I will definitely let you know what I think when I get further use in it. :) Until next time, happy reading.