Well the kind of karma Im talking about is the kind that is spoken of by Buddhists. Buddhists see desire as the force that causes suffering in the world. So if your motive of doing a good deed stems from a personal desire for something (good fortune) than you arn't really getting good karma. Thus if you see your good karma as a bank account to be filled up for yourself, you are missing the point. Karma is the force that keeps the world in balance. I think. Somebody might have to look the exact definition up. Does this make sense?

Basically do good and don't expect anything in return. Do it because it is the right thing to do, not because karma might reward you for it later.