Affiliate marketing has grown quickly since its inception. The e-commerce website, viewed as a marketing toy in the early days of the Internet, became an integrated part of the overall business plan and in some cases grew to a bigger business than the existing offline business. According to one report, the total sales amount generated through affiliate networks in 2006 was £2.16 billion in the United Kingdom alone. The estimates were £1.35 billion in sales in 2005. MarketingSherpa's research team estimated that, in 2006, affiliates worldwide earned US$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 advertising programs.
This is the question that gets asked the most, but it's the one with really no answer. It depends on a lot of variables, so you can make anything from zero to tens of thousands of dollars per month. For me personally, I don't make that much from Clickbank, and never have. I take in about $100 per month. It isn't impressive, but I'll explain more about my stats below.
Two-tier programs exist in the minority of affiliate programs; most are simply one-tier. Referral programs beyond two-tier resemble multi-level marketing (MLM) or network marketing but are different: Multi-level marketing (MLM) or network marketing associations tend to have more complex commission requirements/qualifications than standard affiliate programs.