Optical encoding of data is quite common - bar codes and the 2-D shipping codes on UPS packages are two of the most common examples.

2-D "Quick Response" or "QR" bar codes have been created to transmit larger amounts of information than a standard bar code while keeping a small size. This technology has been gaining popularity in Japan for the past several years and is now coming over to the US. The Google Android OS version 1.6 features QR output for contacts.

Why are they on the business cards?

Business Cards are used to transmit information, and many times are tossed without the information ever being placed into anyone's contact database. By putting the QR code on the business card, the information can be transmitted in a form that's simpler for the user to store and catalog.

The following pages provide additional information on QR codes and the software/phones needed to use them.

Link to the generator used on the business cards
http://zxing.appspot.com/generator/

Links to software for camera enabled cell phones.
http://reader.kaywa.com/
http://zxing.googlecode.com/files/BarcodeScanner3.01.apk

Code for the android reader
http://code.google.com/p/zxing/