My University (The University of Kentucky) actually just implemented this this year. We scan the codes and we can either go to a webpage or download an app that has the GPS location of the buses with ETA. Pretty cool, actually.
There's a project here in my town by a couple of my fellow engineering students working on a related idea they're calling awesometouch. They've installed a few in our city already as far as I know.
I don't believe they're running Android, and the machines are pretty special purpose, but still similar in concept as far as huge touchscreens go: http://awesometouch.org/
I miss going to class with a floppy and knowing it was corrupted, get an extension on the assignment. I am only 20... are there really computer users out there unfamiliar with floppies? I keep 5.25" drives around for fun and I still have Windows 95 on 3.25"ers :)
I dont think he is stressing the ease of doing this with credit card numbers. The sample space he is suggesting generating is far too large... You can usually identify the first several digits simply by the issuing organization, as they all use standardized numbers, the remaining digits must pass a certain checksum algorithm. So really generating a bunch of valid cc numbers is quite trivial. Matching exp dates with numbers and ccv numbers.. Different story.
But i wonder what the limits to effectiveness is on this attack. I usually randomly swirl around with a smear tool to blur out things...
Also, as far as your input filtering goes, I enjoy the 2001: responses. But you're not picking up extra "$" characters for it. It gives me an answer for "$$$$$$$$$$$$$$$$$$$$$$$4" and "$$$$$$4$$$$$$" and "$$$44$$$4$4$", for example.