Lamont is right in that QR codes are basically used on printed media. If you're already on the web using your computer, smartphone or toaster then a QR code is pretty worthless.
We create them and put them on the back of business cards all the time- which is a handy way to get contact information into a smart phone. Instead of having to type the persons info into your phone, you can just scan it and then hit ADD to contacts. To do this the QR code has to be set up in the right format, preferable in VCard format.
Here's an example of my Vcard QR code:

The above code contains my name, address, phone, fax, cell, email and website. Some QR codes will simply link to a website that has your info, which makes for a more simple QR code - but the person then must have web access for it to work. I prefer a code that actually contains the data. All it takes is a scan and ADD to put someone into your contacts. Pretty slick.
I guess it could be handy on a website for getting that kind of information into your smart phone too.
There are various scanner apps available for smartphones, and not all work the same. Some handle the Vcard format well, others do not.
The best ones I've found so far:
Optiscan
i-nigma
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