bookmooch is John Buckman’s other site where people trade books for the cost of shipping. I’ve found a small paperback costs about $2 to ship in the US and have started posting my library for moochers. A really interesting side project is called BM Journals which is essentially a ccMixter for the analog world. That is, people pass around a blank book and add a page of goo to it until it fills up. John blogs about here.
For recording topics it’s a little difficult to go too broad because searching for “studio” gets you movie stuff, “audio” gets you every book ever committed to books-on-tape and CD, “music” is useless, etc. But if you get more specific like “Ableton” the results are a little promising. (Looks like somebody was trying to mooch a copy of FL Studio, the software, not a book)