The Ubiquitous QR Code (in Japan, anyway)
Anyone who has been to Japan already knows this, but these things are everywhere. Yes, I eat fast food sometimes. So what?
There have been a lot of alternatives springing up over the last couple years, especially in Europe, but in Japan, along with "empty mail" "quick-response codes" the easiest way to get to a URL. It's also used for getting calendar events, contact info, etc. They were originally developed for shipping purposes. Nearly every Japanese keitai comes with a QR-Code reader. They are on you food wrappers, beer cans, sides of buidings, in subways and taxis, on clothes, in museums and restaurants, etc. You can see for yourself here.