I use Booklending.com mainly and also Books for My eReader and currently have approx. 300 eBooks up for loan on the first one. Mostly these are eBooks that were free at one point or another. It seems like all the people wanting/waiting for my books are those that want to borrow lots of titles and don't bother posting ANY books to lend to others.
I personally have quit lending to borrowers who have not bothered to list anything. These days it is so easy to find free books to loan to others that they are just being lazy.
Most of the people borrowing from outside the US don't check to see if they can actually buy the book from their Amazon. ( A requisite for actually borrowing the book in their country. If it isn't for sale, they can't borrow it)
So many of my books were sitting in pending after being loaned to someone who requested the book and then coming back after 7 days because the borrowers weren't actually taking the loan. That is when I started being more careful on choosing the people I want to loan to.
I really feel that the two sites I use for borrowing are slowly losing active members. At some point I do feel that they may fold.
These are all my own opinions and lending methods. Probably will make some people angry. Oh well.