Researchers from UC Berkeley and University of San Diego have conducted a study on spam based marketing, "Spamalytics: An Empirical Analysis of Spam Marketing Conversion" and come out with very interesting results.
The paper was presented at the 15th ACM conference on Computer and communications security which was held on October 27-31, 2008.
The study was conducted by infiltrating storm botnet and inserting two websites in the botnets link indexes. So the researchers were basically sending you spam, which was harmless, to study how these botnets operate and the profitability in such operations.
The study found that viagra raises the expectations of many and e-greeting cards are good vehicles to deliver botnet agents. Almost half a billion spam emails were sent and it is estimated that around 25% of these reached the users email boxes and actually small fraction of these reached the site. But they did make sales (Pretend) and managed to deliver more bots to the net, again pretend. So the shear number of bots in the stormbonet and based on who is selling what, spam marketting is profitable but not in millions of dollars in a day.
I suggest you read the paper published by researchers that gives a good education on how these spam botnets operate and how our preventive measures work. Even the experts will learn a thing or two.
"Spamalytics: An Empirical Analysis of Spam Marketing Conversion"