I haven't actually gotten any complaints on the little offers like the "Give us your email address and you might get a $500 gift card if you complete 100 other offers." That's a whole industry unto itself that is in trouble...

The major fraud seems to be coming with things like Scholastic, Blockbuster, all of those Hoodia and Sleep things, Passport to Fun, etc. Essentially the ones where you pay a small amount for something to get a whole lot more back.