I don't know about other people but I find that adsense is not my biggest money maker, however it is a good test of how targeted you visitors are, let me explain. I have a few affiliate links around my sites, they target products and services that readers may find useful. They get clicked on once and a while and sometimes something is bought and I get a little cash. What I have found is that when I write something it changes the dynamic of google adsense posts, when the posts are getting clicks (aka the ads a relevant) then I am finding a strong correlation that purchases are made through my affiliate. I'm not one to try to drum up false correlations, but it seems to be true. If your targeting your site correctly, adsense will let you know. Which is useful as many affiliates don't credit your account for 2-3 days after the purchase (I guess it takes time for them to verify/ship so thats when they finish the order?)