Interestingly, a NY Supreme Court judge ruled yesterday that there's nothing wrong with a juror drinking - or being drunk - during a trial and during deliberations. (NY Times article - subscription required)
I seem to remember the 1987 U.S. Supreme Court case referred to in the article from a law school class. There were allegations that the jurors were drank, smoked marijuana and used cocaine together and that the entire affair was "one big party."
I guess there are case where it could work out in a defendant's favor. I'd love to hear a juror say, "Hey, if I can drink and deliberate responsibly, there's no reason the defendant couldn't drink and drive responsibly. Not guilty."