I'm delighted at this request, since much progress on this feature was already made, and we hope to have it ready in the near future.
at the moment the system is based on personal collections and personal friends, but we want to make it more communal, hence "shared libraries" - anyone will be able to open any number of shared libraries, and invite other users to them. users could also request to join those. users in shared libraries don't need to be friends on the site, just being in the library means they can see and publish items on it and request to borrow them.
this feature is 80% done and waiting for the completion of the email notifications and messaging.
thanks for the suggestion, it's nice to get this king of feedback.
Yonatan