I remember one time I went to a party with a friend, and he was supposed to be our designated driver. He started drinking as soon as we got to the party! He said it wasn't a big deal if he had one or two beers...
Looking back, he was probably right - it's not the end of the world if someone is careful to time a drink or two against the passage of time. For me personally though, I prefer to abstain completely if I'm driving a car later. I've learned over time though that most people don't seem to agree with me!
Do you ever drink a drink or two and then once enough time has gone by, drive home?