I just finished my taxes. Turbotax gives you the option of receiving all or a portion of your return as Amazon credit + 10%, up to something like $10,000. (i.e. I divert $300 of my return to Amazon, and it appears as a $330 credit.)
While I don't purchase a significant volume of goods on Amazon, it is the cheapest place for me to buy several things throughout the year, and especially around the holidays I use it quite a bit.
I did some quick math, looking at past years' Amazon/online expenses and adding up the items I am thinking about buying this year or at least in the near term. I diverted that number to amazon with a few clicks.
With essentially zero effort, I just cut 10% off my holiday shopping and most (if not all) of my internet purchases in 2015.