From Wickipedia... According to one report, total sales generated through affiliate networks in 2006 was £2.16 billion in the UK alone. MarketingSherpa's research team estimated that, in 2006, affiliates worldwide earned $6.5 billion in bounty and commissions from a variety of sources in retail, personal finance, gaming and gambling, travel, telecom, education, publishing and forms of lead generation other than contextual ad networks such as Google AdSense.
That is good to know. Gives you a bit of motivation.. knowing that you can have a piece of that $6.5 Billion