Unfortunately, I imagine it'd be a fair bit of money. Many toolbars track every site you visit, how long you're there, what you type on the site (including personally identifying information), and a host of other Orwellian things.

I can't imagine anyone feels good about trying to trick their users into installing this crap. If the money wasn't good, only completely amoral psychopaths would do it. As it stands, the financial incentives bring it to the point where greedy asshats are also willing to get in on the action.