Yes, I see I should have blogged about this, instead of airily dismissing it and turning my attention to a dark corridor of the Google Calendar.
Briefly, then: I once explained to a Haddon reader that non-delivery of our reminder notices did not excuse the late return of borrowed items, and told him, & then everyone else in an email circular, that I made a note of return dates in my filofax. The next person who tries on the undelivered-reminder ploy will be referred to the libraries widget, which takes the work of making such an entry.
And even more briefly: I wish I'd noticed, before the airy turn, the extra extra thing of the Libraries at Cambridge calendar. Now I don't need to go tramping through CamTools in search of journal discussion lunches.