Careful, there were some sites offering laptops and Ipods for reading emails and filling in forms. People did so for months saving credits, but never saw their items. All of a sudden the site was down, and never seen again. Making millions for the owners (getting paid themselves for all the advertising, mails and forms), I can't recall the name of that service, pay-per-click or something like that. And of course all the email addresses of the participants were sold to spammers.