_Magistra et Mater_ in book form.  (Well, not really.)

Why _don't_ libraries have a "people who checked out this book also checked out..." feature? (Also, I suspect other peoples' tags become most useful when employed as features in a recommendation system, rather than directly searching on them, but that's a mere guess.)

"(Attention Conservation Notice: this is an unholy mashup between historical speculation and experience from 23 Things, exacerbated by too much checking footnotes and not enough sleep)."