Make those cards work for you! I use a discover card to pay every bill and with every purchase. I average between $80-$110 a month in free money. The kicker is that at the end of my first year using this card they double the rewards for the entire year and pay it to me. Basically now $160-$220 a month. Boom!
Boom is right my friend. Thats some serious extra money for nothing.
I change cards about once a year maybe 18 months. It's worth it to put a little research time in. If I liked to travel then the rewards would be just crazy, I prefer my own bed though.