The image above should be the QR - Quick Response code for this Google blog. I am not too great at using mobile or cell phones as they're called in the USA. However, I do believe that QR codes can be useful.
I have had qr codes for my other sites placed onto double sided business cards. I conducted a test the other day. I had asked one of my friends to scan the qr code of one of my business cards. The test proved to be a success as my friend was able to go direct to my site without having to type in the web address. This saves valuable time. I will conduct a similar test for the qr code for this blog as well.