In Europe many stores hand out coin-sized plastic tokens that unlock the cart. You still want to get your token back at the end of a shopping trip, though, and take the cart back to the cart queue (which I assume is the real purpose of the coin lock things).
I was head of an IT department at the time and distinctly remember telling everyone in a team meeting that this "micro-blogging" was pointless, going nowhere and we should ignore it. Wrong!
Ha ha! Well done!