ember - 10:47 pm on Feb 28, 2013 (gmt 0)
I reduced most pages to 2 ads, as I have read in many forums that putting too much ads per page would compromise the quality and relevance of the ads.
I believe that has to do with how much content is on the page. I have 3 ad units on many pages, and the ads are very relevant and pay well. But they tend to be on long pages with a lot of text.