According to 2d code, a blog about QR codes and bar codes, the 2012 London Design Festival includes a sculpture that is a QR code made of chocolate. If you scan it with your smartphone’s QR scanner, you are rewarded with a voucher for a free sample box of chocolate from Hotel Chocolat.
I tried it, it works! I got my voucher. Only problem is that you have to go to their shop in Covent Garden (London) before 9/30/12 to redeem it. Darn, not in my current travel plans.