A great quotation from Charles Stross's book Toast about spam and spammers:
Something the junk advertisers don't seem to understand: we live in an information-supersaturated world. If I don't want to buy something, no amount of shouting or propagandizing will budge me; all it will do is get me annoyed. On the other hand, if I have a need for your product, I can seek it out in an eyeblink.
-- from the short story, TOAST: A Con Report, by Charles Stross