When I got up this morning, I had no intention of designing any sort of rule or definition for drunkenness in the game. It's been a thorn that's been around a long time without my having any reason to address it. Now, however, I do have full rules for it - and they are simple, straight-forward and adaptable to any campaign.
I was a little worried about the "how do you determined intoxication" problem, but that's behind me now.
The manner in which a character becomes inebriated to varying degrees begins with this table:
The numbers listed under each character race indicate the saving throw that must be made if a 'drink' is taken (according to the character's weight). A drink is defined as 2 ounces of spirits, 8 ounces of strong ale (as opposed to a short beer, an ale-like drink made without hops) or 6 ounces of wine. Once this amount has been consumed, a saving throw can be made to determine if the character has increased their inebriation or not. Only one saving throw must be failed for the character to become flushed. It requires two failed saving throws altogether for a character to become tight (counting the one that made the character flushed). It requires three failed saving throws to cause a character to become smashed. In each case, the saving throw is adjusted by constitution as noted.
Where time is a factor, the character should roll a d6 to see how many ten minute periods it takes for the increased inebriation to take hold. For example, a male dwarf weighing 155 lbs., with a 14 constitution, fails to roll the necessary 9 on a d20 to retain his present sobriety. However, though the greater inebriation is now inevitable, it requires 1d6 x 10 minutes to pass before our dwarf feels these effects. We may imagine that he rolls a 4, indicating he will become flushed in 40 minutes. However, our dwarf continues to drink during that time. He has another glass of ale and fails again, approximately 30 minutes before he is due to become flushed. He rolls a d6 again and now he rolls a 1 - indicating he will be tight in 10 minutes. When this case arises, presume that the character will move from sober (none of what he has drunk so far has had any notable effect) to tight all at once, once the ten minutes have passed. Where conflicts occur, consider only the result where the greatest degree of intoxication will occur.
There is room on this system for other forms of intoxicants, such as mead, dwarven ale, etcetera. Simply assign an amount in ounces for such that defines that beverage as a "drink" - then roll a saving throw accordingly when that amount is consumed.