I created a simple Drupal module that will allow someone to enter in their contact information and generate a QR code that can then be scanned in to quickly and easily add someone's information to their address book.
There is a dependency to the Chart Module that uses Google's API to generate the QR code image.
There is a demo you can check out here to generate your own: QR Code Generator
Note: this is more or less a simple proof of concept and hasn't been released. If you're looking for a full-featured module check this one out Mobile Codes