Do you know if there is any published work about spam? Some research about why some companies do spam, or about how consumer perceive spam? (& more generally opt-in/opt-out)

In some recent work I was commissed to do for a company called Surf Control on privacy and surveillance in the Australian workplace, I found that 75% of Australian workers receive spam. Of the types of email they found to be objectionable: 74% - offers for email lists 88% - credit offers 87% - money making offers 90% - chain 17% - jokes 77% porn Regards Monica Whitty