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There is a fantastic article https://www.uie.com/articles/three_hund_million_button/ https://www.uie.com/articles/three_hund_million_button/ and followup http://www.uie.com/brainsparks/2011/10/17/the-back-story-for-the-300-million-button/ http://www.uie.com/brainsparks/2011/10/17/the-back-story-for... about the $300 million button. They showed just how much forcing people to register actually costs, and stats on how many accounts people had, how often they remembered which one was used etc.