Complained to Amazon about the subject spam when trying to search in the Kindle store, got paid $10
I had a few spare minutes and complained about how inaccurate the categories are, with fiction all over nonfiction, porn all over art and photography, and so on, pointing out that it wastes user time and makes them give up searching for books. (To clarify, I don't have anything against porn, I just want to be the one who chooses if/when to see it.)
I asked them when they were going to solve the problem and they said "Soon" (yeah, right), but without my asking, they gave me a $10 credit. That made me think that if a lot of people who are frustrated by this complain, they might end up paying attention and actually fixing the problem.
I've also been flagging indvidual titles with "Report a problem," saying that the information is inaccurate. If even just a few hundred of us keep flagging content, that takes up enough time for them to process and generates enough reports that it might get fixed.
The solutions would be so easy -- don't allow more than three or so topics per title, don't allow a book to be listed under both fiction and nonfiction, and set up a filter for erotica so that folks can choose whether or not to see it. That would probably take care of 80% of the trouble.