Book trade services?

Anyone use online book trading services? Frugal Reader is one I just came across (you ship books to other members in exchange for books from others, paperbacks are 1 point, hardcovers 2 points, you pay shipping), and I've heard of another though I forget the name now (you get a monetary credit to your account each time you send in a book, each book is worth a different amount, I forget if you send directly to other members or to the webpage owners). Any of these any good? My questions include:

* Is it free?
* Can it print shipping labels?
* How fast is turnover of a book you list?
* How reliable is the shipping?
* How/when does it release your address to the shipper (if another human)?
* Does it do audiobooks?
* How does it value books?
* Can you unlist a book you own?
* What if you don't get the book?