Quick Response codes or otherwise known as QR Codes started showing up in marketing here in Edmonton about 3 years ago. Originally created back in 1997 these were primarily use for tracking parts in vehicle manufacturing but are now used for a wide variety of purposes. Whether or not those purposes are useful to the end user is another question. In my experience, QR Codes are best used to give an end user direct access to something they may be looking for such as information on a product, a form to enter into a contest, or a link to download a newsletter, ebook, audiobook, etc.
QR Codes can also make excellent editions to business cards with information already filled out and added to a client's address book with minimal or no fuss. They are also handy for connecting to an encrypted wifi network (Sorry, Android only). However QR Codes can and have been horrifically misused, such as having a QR Code in an ad that doesn't go to the the product advertised but a cheap useless landing page or the companies website. Another example I've seen are QR Codes on realty signs that go to the realtor’s website instead of the property that is for sale.
The QR Code empowers the user giving them instant access to something that they are doing, wanting to do, or get information on. They can also be used to contain information like your library card number, an address, phone number and event information. It also adds a bit of interactivity between you and the user, getting your proverbial “foot in the door”.
My favourite QR Code Generator is http://www.qrstuff.com and you can customize the colour of your QR Code without using a graphics program like photoshop, it's free and easy to use.
Recommended QR Code Readers:
Some other good information on QR Codes: