Didn't the United States Postal Service try this years ago?
Isn't a huge amount of spam these days generated by zombie computers? So who gets charged then if your computer has become a major Spam e-mailer?
Granted, I half don't care if people who let their machines GET infected by such things have to pay money for their laziness/stupidity but it hardly seems fair if it's somebody's mom who probably doesn't know any better.
-Kevin S

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic