We now have 5 people in our carpool and I have really been enjoying the camaraderie. Since different people are riding and driving every day, it's difficult to keep track of who owes who a ride. I invented a system where each rider gives the driver one of his business cards whenever he rides. When the rider drives, he gets his cards back from whoever has driven for him before, or else they give him one of their cards. So far it's worked very well.
Considering the money I've saved on gas, the new friends I've made, not to mention the nice prizes you offer, it's well worth the small inconvenience of working to a more rigid schedule.