I found this table on Pubmatic to be fascinating: http://pubmatic.com/adpriceindex/index.html It lists average eCPM based on size of your site. I think it brings it down to earth after hearing about people bragging that their 20 sites are making them $250/day each. It's nice to know what can be reasonable expected.
I have sites making $20 CPM and sites making $0.50 CPM, so it can vary a LOT more than the averages listed there. It is an interesting link that you posted, particularly the drop in CPM over time...