In Is the Earth 6000 years old? there is a downvoted answer that references a book available via amazon with usual book hype:
"In a sentence: If even a small part of this is true it turns evolution on its ear."
There are two links:
http://rads.stackoverflow.com/amzn/click/0892132949, which when clicked will bring up amazon with what looks like some kind of referral id as part of the URL (this technique strikes me as very 1990s though, so makes me wonder if its real or not).
I appreciate that Stack Exchange needs a way to make money.... but I am somewhat skeptical that they would insert an answer into a question to help sell a book. Product placement (especially automated product placement) within answers will probably just annoy people. A related books ad box on the side wouldn't be as intrusive, but I think I'm a preachin' to the choir and everyone knows this already.
Any idea what is going on here?