How about making the world a library? With books everywhere! This is the the precise plan of the BookCrossing project. The idea is simple: books get an id, are registered on the website of the project and put anywhere you want in the real world. Anybody else who finds the book can read it. Ideally the finder sees that the book belongs to Bookcrossing and reports the book as found.
Bookcrossing village library caught my interest and will come with me to Heidelberg. They will be read and then placed somewhere.
Some of my questions were also answered by project members. For example, how many of the books are reported as found. This depends on different factors like where you place it. On average around 10% but some guys place the books in better places (e.g. in fridges at IKEA) and have report rates of around 30%.
So if you have old books you don't need anymore or books you really want to be read by others: Free them!