The company's Click Fraud Index is worth a look to get a sense not only of growth rates, but also of geographic locations launching the click-cons.
Needless to say, stats like these set the big charge-for-clicks companies' teeth on edge, as witness this interview with Google click-cop Shuman Ghosemajumder, and this Click Forensics response interview, both from Forbes last year.
Click Forensics' current fraud findings are here.