I happen to know this because of a great article on the subject that I just read: Top 14 Things Marketers Need to Know About QR Codes by fellow Search Engine Watch columnist Angie Schottmuller. This article appears in the April 26 issue of Search Engine Watch and they bill it is as: "a great crash course on tools, tactics, and best practices to confidently help you jumpstart a 2D barcode marketing campaign." And I agree wholeheartedly.
The article is also a good general introduction to the technology and why people are using it. Since one goal of this blog is to make technology more accessible I thought I would highlight Angie's article for that reason. And that makes one less article I have to write, which is good, because I know that someone, at some point, is going to ask me: Stephen, what's a QR code? Now I can simply point them in Angie's direction.