The BBC ran a story today about how spammers make money. They estimated that with a click through rate of just 0.00001% it could be possible to make up to $2 million a year.
At work we deal on click through rates of double digit percentages and yet somehow don’t make $200 billion a year. The downside of being all ethical and using an opt-in list. 
Meanwhile I got this spam in my akismet cesspool:
Hi there!
My first post at this great blog!
I wanna show u my dayly updated blog: [adjective adjective verb noun]
Have a nice day!
BB!P.S. if you don’t want to see this message please write me to [email] with subject “NO ADS” and URL of your forum
Thank you for cooperation!
Allowing for the fact that 1 in 100,000 people are stupid enough to buy drugs from a spammer, how many webmasters are stupid enoiugh to send a forum URL to a spammer?