The rates are $1.00 for every 1000 ad impressions your site serves, which is pretty slim to say the least; sure it could add up over time - at 5,000 impressions a day you're pulling in $1,800US a year so don't quit the day job yet. It sounds to me like they're giving you a small percentage of the money they're already making off the annoying banner ads that are served from your Web pages anyways.
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