If you look at the traffic details for the domain below, it says

"People who are interested in merged.ca also bought:"

and then it looks like it cross-references Alexa toolbar data with Amazon shopping history. I don't see it on many other domains, including dp or wmw (the lists would be huge) but I did see it on revenews.com's listing. It is scarce and also pretty strange that they would mix the data like that as the relevant clickthroughs are probably pretty low.

http://www.alexa.com/data/details/traffic_details?q=merged.ca&url=merged.ca