Greg, i completely agree with your point on personal responsibility of everyone when using its PC.
If we take even deeper look at the problem, we'll see one more layer of the disease-symptoms pair. In this layer the Disease is the lack of information about subjects of popular spam offers and the symptom is the spam offer itself. For example, I think a lot of people buys pills by spam offer just because they not well informed about side effects of such pills -- this is the disease, so they're ready to respond to corresponding spam email which is symptom in this case.
So even if you have successfully deleted all today zombies from PCs there's always be a lot of people who still continue responding to spam and so installing new zombies on their PCs. And even worse. New generations are growing continuously and one of the educational system task is to explain children what is spam.
I think these two problems must be solved together. Then we can say there's a hope to overcome spammers.
So we need anti-spam campaigns explaining people why this game is so tricky.