Answer:
No, swaptree is not a scam. I have been actively using swaptree for about a month now and I have made about 6 trades so far and I love it. I've been able to get rid of books and CDs that I don't want anymore and I trade them for books and other stuff that I do want.
Keep in mind that there will always be people out there who will try and scam you, but that exists everywhere to some degree. So far I haven't heard of any specific scams through swaptree.