Spammers are not very effective. We all know this from personal experience. Which of you actually ever responded to those mails by VIAGRA and Co?… Correct. None. There are no valid numbers on the effectiveness, except this one BBC article.
Thus the Conversion Rate is: 1: 12,500,000
Sounds ineffective, right? Looking into the numbers: For one conversion, a SPAMMER would need to reach out to EVERYONE in L.A. to sell ONE product. Would this kind of conversion be anything but annoying? No… For example, to fake a grassroots movement from the size of the PIPA and SOPA, a spammer would need to send 8,000 mails to each and every person on this planet…
Admittedly, the BBC numbers are old. On one hand, SPAM attacks on social networks are said to be more effective then via email. On the other hand, people got more and more used to SPAM and started to cope with their funky promises even better.