1994 was the magic year for the QR code.  However, things had started before that time.  Japan was the first country really to get excited about the little stamps.  There is a slide presentation that gives the information nicely, although there is one slide some may find objectionable.
They are now growing in popularity in the US, because of the mobile phone/ smart phone and how much data they can hold. 
Here is a little video recap of the above.

Unlike a regular bar code that can only have data in one direction, QRs are 2 dimensional, holding up to 7,000 characters.  This is a bit misleading because the more information attached to the code, the more chance that the reader will mess up.  Rule of thumb, approx 300 characters will allow quick response from a reader.

Currently, QRs are being used for:

Why use QR codes?

QR code in Instruction