David Bainbridge and Ian Witten of the University of Waikato in New Zealand published a paper last year about using the Greenstone digital library toolkit to help offline XO users share libraries of books. From their abstract:

The idea draws upon mobile libraries (bookmobiles) for its inspiration, which first appeared in Victorian times. The implemented technique works by building on the mesh network that is instrumental to the XO-laptop approach. To use the technique, on each portable XO-laptop a version of Greenstone is installed, allowing the owner to develop and manage their own set of books. The version of Greenstone has been adapted to support a form of interoperability we have called Digital Library Talkback. On the mesh, when two XO-laptops “see” each other, the two users can search and browse the other user’s digital library; when they see a book they like, they can have it transferred to their library with a single click using the Digital Library Talkback mechanism.

Alas, you need to be an ACM member or pay $15 to read the full paper.