Viagra etc aside, I don’t consider one or two targeted mails from an aff program spam. If they are bulk and don’t mention some detail about my site, they get a cursory glance before deletion, and I have very rarely responded to one of these. It would have to be a great coincidence of timing and content to be acted on.
If they show much more often than that, they get trashed without a glance, and the sender name sticks with me as an annoyance. I get so much legitimate daily mail that repeated spam becomes an annoyance at best.
If the mail is personal and shows someone actually bothered to look at the site, it gets read. If it is of interest but not right now, it gets filed. When looking for new programs, I look at these files.