Jimbo,
The Cablecard option will take the place of a cable box with two limitations. First, it will only work with the TV it is assigned to and can not be moved to a different TV. Second and more important, it only provides one way communication to the cable system. That means with a cable card no On Demand or Pay per View as you can not send information to the cable system. That means no late night porn..
I have also read that CableCards sometimes have setup problems.
If you don't have an issue with the sie of a cable box, I'd keep it.