While 2011 may technically be known as the Year of the Rabbit (at least according to the Chinese Zodiac), the past few months have surely been the summer of the QR code. Created more than 15 years ago, these pixelated geometric designs are now popping up everywhere from Taco Bell to graveyard tombstones to hand-painted scarves and beyond.

With nearly one in five people in the U.S. using some form of mobile Web device each day, it looks like QR codes (along with other 2D barcodes ScanLife, Jagtag Datamatrix and Microsoft Tag) have moved from the realm of tech fad to necessary evil. But before you jump on the wagon and start tacking black and white squares onto all of your promotional items, take some time to learn what works (and what doesn't) for these 21<