I am not personally affected, so I can see the bizarrely funny side of this particular bit of incompetence: hey, Amazon, if you're trying to pretend you're just not giving Amazon rank to adult books, you are so doing it wrong.
(That link is to Shayla Black's DECADENT, a book which is, um, rather heavy on the, er -- yes, well. And ranked #344,701 in Books!)
List of affected books is here -- to me, the big surprise is that there's just no way Amazon could even think their excuse would fly for a second. I mean, guys. The Well of Loneliness. Adult? Really?! Man, I wonder what happened with this decision. Oh, to be a fly on the wall there.