I didn't know there was a difference... but we've got a blue Discover card. Says on Chris's link that's the Open Road card. Bonus on gas and groceries, I think. We get the cash back in gift cards, usually... because there's an extra multiplier. $30 for $20, etc.
We put anywhere from a few hundred dollars to several thousand dollars on it every month, and write them a check when the bill comes. They basically pay us several hundred bucks a year to use their card.
I know I get a free pair of Revos about once a year thanks to them.