The only thing that would be interesting about this is if the Blippy card gave you 1% off of every transaction. Suddenly you'd face a tradeoff between privacy

The only thing that would be interesting about this is if the Blippy card gave you 1% off of every transaction. Suddenly you'd face a tradeoff between privacy vs. getting a discount[1]. That 1% could almost certainly be made up by analytics and viral referrals. If someone saw your stream and clicked on say an Amazon book, then Amazon easily makes that 1% back. In fact, for some companies the discount could be substantially more than 1%. [1] Importantly, experiments have shown that privacy is dear but cheap. I recall an experiment where people stood in a busy area and paid people $10 for their username and password. Many took them up on it.