I didn&#x27;t see anything along these lines in the article, but I  remember thinking during my undergraduate studies that it would be cool to be able to opt-in to a program that gives a list of people who had checked out the same books (or perhaps the same `n&#x27; books) as you. I can&#x27;t recall the exact title, but there was some relatively specialized book on dynamical systems I often checked out that kept getting recalled. I wondered: who is this person that wants this book and can we go get lunch together?<p>I guess that there are potential privacy issues here (although perhaps surmountable with an opt-in system) but it still strikes me as worth looking into (either for regular libraries or for sites like Amazon).