[DolphinChicaDDD]

This is the system we set up (and I commend you guys for getting a head start on it...took us about 2 years). This is only in effect for mixers.

First, we get a master list of all those who have a car. Technically, you can't tell a person who is 21 that they have to be sober; its their right to be able to drink. But their name goes into the hat anyway.
A sign up sheet is passed around for mixers; anyone who wants to be a driver volunteers. Usually, there is enough people who want to drive/ have to be sober for some reason (that was usually me because of the 48hour rule for sports...and i used to bring my text books with me and take over one of the guy's rooms).
If not enough girls volunteer, names get drawn from a hat. If the person is over 21 and doesn't want to drive...well, there isn't anything that can be done about it. If you pick a girl under 21, she is DD.
We also put a time limit for mixers. After 2am, you need to call yourself a cab (unless the DD agrees to come back).
Some events we just get drunk buses. We actually get discounts from one guy cause all of us use him on the weekends.

ETA: I think anything that prevents a drunk person from getting on the road is a good thing. Like other people said, people will drink.