Could not find anything when I Googled about How Big Affiliate Marketing Industry is and so would love to get some numbers like growth numbers in 2011, 2010, and past and how is the future of this industry shaping up. I see every ad network allows affiliate marketeers but when they outgrow affiliates, they just kick them out. It happened with Adwords, It happened with Facebook and soon it will happen with Bing may be.
All I can is it is very big because there is lot of money being made by lot of individuals but then those type of individuals are few and far between because they are more affiliates you fail to make a dime than those who can make a fortune.