At least twice before I've chatted with people about the idea of sharing books. I've been thinking about it again now that I've joined the NCTM publishing committee. We get copies of all the new books plus copies of books that were published 5n (n=whole number) years ago. It's a lot of books and my office is small. After reviewing books we're welcome to do what we want with them, so I'd love to share the wealth with all of you!
In past conversations we've discussed some fun ideas like making notes in the margins and leaving a note in the front flap so you can see who wrote the notes and/or creating a blog or hashtag or something to share reviews. Since it's my new years resolution to "just say no" I want to make this work without having to do any work! So instead of doing something new let's just use already existing tech.
If you have a math ed book that you want to share with someone add it to http://www.paperbackswap.com/ with the hashtags #MTBoS and #MTBoSwap in the keyword section. Then post it on twitter with #MTBoSwap so people know this is a thing!
If you want to make this into something cooler than just sharing books please go for it!