I’ve never seen any of it myself, but I knew a librarian that was developing quite a collection - more out of amusement than prurient interest (at least that is what she said).
From what I am told, it plays off of most of the “librarian” stereotypes; except for the middle-aged woman stereotype.
Mostly it plays off the idea of a sexually repressed woman (and it is true that way too many people actually believe that librarians are, as a class, repressed) giving in to her repressed desires. I would imagine it also plays to a fantasy of having an intelligent, logical woman reduced to animal passions.
I made a contribution to the librarian genre… of course, I portrayed myself as the librarian, which is what I was at the time (although not middle aged, conservative, or a woman). Here it is: