For the past couple of years I've been collecting Star Trek novels through various sources such as thrift stores, used book stores, buying lots through Craigslist and eBay, etc. Through this process I've often had to get duplicates of books in order to get the books that I want in a lot (and I've also accidentally bought books I already had not realizing it until I got home). That being said, I have many, many duplicates that I have absolutely no use for that I was thinking about listing on Paperbackswap.com but after thinking about it, I'd much rather do exchanges with other fellow Trek fans on this board.
It would work like this: you post the list of books you want to get rid of (and if you want, titles you want) and then you check the other lists posted to see if there's anything you want and you work out a trade. There would be no charging the other member anything and the only charges that you would incur would be the shipping charges to the other member. Ideally it would be 1:1 situation with all books being equal (regradless of title, or whether or not it's paperback or hardcover) but obviously members would be able to work whatever deal they want.
The only way this can work is for everyone to be honest, so if you make a deal, you have to follow through.
If you like this idea, chime in and post your list and mine will be forthcoming.