Is nothing so sacred as the ritual of shotgun? I think that it's truly a pure game, but I guess even the purest of games has its sophistry. Our rules say that you have to be able to see the car and be on your way to it in order to call shotgun and that all parties riding have to be able to see it, if they tried (ie, no bags over people's heads or anything).

If the driver's significant other is going to accompany the group for the evening, she is automatically given shotgun (unless she declines the shotgun responsibilities...) :)

Tom Tolworthy was nice enough to send along the Official Shotgun Rules. Truly a labor of love. I wish I could make icons like that. Anyway, I guess the "Everyone has to be able to see the car" rule is not part of the official spec, although the significant other rule is there.