An interesting article regarding the effect of credit card spending, this study indicates that using a credit card changes our perception regarding the value of the goods we are purchasing.
While I'm waiting for studies as to the debit card effect, I thought the discussion of other payment systems, i.e. Google Wallet and smart phone apps, intriguing. I have one click purchasing set up through Amazon.com for my Kindle and it is, indeed, very easy and painless for me to buy e-books. My book buying expenses went way, way up when I got my Kindle.