Guinness created this brilliant QR code pint glass in a cool marketing effort. When you scan it, "it tweets about your pint, updates your facebook status, checks you in via 4 square, downloads coupons and promotions, invites your friends to join, and even launches exclusive Guiness content."
Wow, that's a lot of networking right there. What's even cooler is that when there's nothing in the glass, you can't see the code at all. When you add a light beer into the glass, you can't scan the code because the background isn't dark enough. But when you add Guinness (or another beer that dark), you can actually use the code.
Link Via BoingBoing