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.
In April 2008 the State of New York inserted an item in the state budget asserting sales tax jurisdiction over Amazon.com sales to residents of New York, based on the existence of affiliate links from New York–based websites to Amazon. The state asserts that even one such affiliate constitutes Amazon having a business presence in the state, and is sufficient to allow New York to tax all Amazon sales to state residents. Amazon challenged the amendment and lost at the trial level in January 2009. The case is currently making its way through the New York appeals courts.