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I haven't really seen anyone talking about converstion tracking lately (where Adwords advertisers let Google know when they've made a sale as a result of an Adsense click).
It isn't just sales. Google lets the advertiser define a "conversion" as a "business action" such as an inquiry, a registration, an amount of time spent on the advertiser's site, etc. This makes sense, because not all AdWords/AdSense advertisers expect clicks to turn into immediate e-commerce or affiliate transactions: They may be trying to obtain high-quality leads instead.
By the way, Google AdWords has a Conversion Tracking FAQ at: