My wife and I pay most of our monthly bills using our Citi Dividend Platinum Select MasterCard cash back credit card. We pay for our groceries, gas, cable/internet, gifts, etc. using the card. We have also arranged to have my Wife's medical insurance bill, my cell phone bill, and our Blockbuster Total Access bill automatically charged to the card each month. There are only a few things that we can't charge to the cash back card such as our mortgages, HOA dues, and auto loans.
We have been averaging a $50 cash back reward every two months since we started paying our bills with the card 4 months ago. It's important to note that there is a $300/year maximum to the cash back rewards. If we reach the maximum, we will then begin using our HSBC Platinum MasterCard cash back credit card. I am currently using the HSBC cash back card for my business trips, to help keep work expenses separate from our monthly bills. I average $25-$50 cash back every three months, just for charging business trips to the card.
It's not a ton of money, but since we're paying the bills anyways, we might as well get a percent or two of our money back. Besides, charging the bills to our cash back card helps with our month-to-month cash flow. And, of course, we always pay the credit card bill in full each month so that no interest is accrued.
If you're not taking advantage of cash back credit cards, you may want to consider it.