An idea to improve service to patrons: Email the patron that has a book checked out, asking him/her nicely to return the item that is needed to fill a hold for another patron when this hold is placed.
I think a lot of systems refer to this as a "recall", but they force a change to the due date (e.g. http://www.library.usyd.edu.au/borrowing/requests.html#recalls) where the patron has to bring the item back within 7 days. I suppose there could be a preference for this though. One, it could just be a friendly reminder. Two, it could be a forced shortening of the due date.
The library suggesting this didn't want to shorten the due date - just to send a nice email asking if the book is still needed. A recall feature would of course still be useful at some point.
*** This bug has been marked as a duplicate of bug 17509 ***