It's actually quite interesting. I didn't know about these guys, but was thinking through this idea a few weeks ago. My version was called "Money Drop". I concluded that technology was cool,but I couldn't think of a compelling reason to use this application, except for 2 cases. 1) Drug dealers and 2) Kidnappers.

Say I just kidnapped your dog and I'm holding it ransom. I email you and tell you to MoneyDrop $100 at the local mall. Once I see the money has been "dropped" I go there and collect it with my smart phone app. Why would this be useful? It's harder to figure out who picked it up since you are in a public space and are just clicking a "pickup" button. Win-win!