I signed up for and used a card a few years back in order to get 2 free flights on southwest - as it turns out, I don't fly very often, and this isn't the best way for me to use the credit card system.
Since then, I've switched to one of the "double miles" travel cards, which doesn't actually give miles, but points, which equates to 2% of spend. I have the 5% freedom card (cash back), which I use for the currently "active" 5% categories, and everything else goes on the 2% travel card. I can then use the points from the 2% card towards hotels and other travel expenses, or on amazon.com purchases. As it turns out, amazon is where I am spending all of my points, and you can get things like laundry detergent on amazon. The only thing I am not sure about is using all of the packaging and shipping resources to buy detergent online, when I could just as easily grab it during a routine store trip and save the world all the trouble of single-packaging it to my doorstep.