Depends on the situation. For example: *if I haven't eaten that day, any alcohol makes me a bit tiddly *the drink available (wine tends to affect me more so I don't gravitate to it) *the situation / my mood, I can be happy to forego drinking altogether - whether I have 1 drink or none makes no odds to enjoyment, generally.
DH and I sometimes drive in to see gigs in the city, and if it's me driving, then I won't drink at all. If I do have one, it will be with food, early on and then followed by soft drinks. I would consider myself to have a high tolerance for alcohol.
If I'm in the US, I am quite comfortable having a drink (or even two, if I'm there longer than 3 hours or so and am having a meal) and then getting behind the wheel. I know my limits, and I choose to either limit myself or take public transit.
In Poland however, where we also have a 0 limit, I wouldn't even consider driving if I've had a drink. They are quite strict about it, and the consequences are severe. That and the language barrier would make for a very fun traffic stop.
I also think that it's worth mentioning that, while I was living in Morocco, no one there EVER had a problem with drunk driving because we all know that no one in Morocco would EVER drink. /sarcasm
Seriously, the drunk driving there was ridiculous.. lots of accidents.. lots of unecessary risk, injury, and loss of life. And no one acknowledges that it is a problem (at least in the community where I lived) because alcohol consumption is so shameful. So it's better to just pretend like no one is doing it.
I don't drive. H will have a couple of drinks if we are out and we have to drive, but this is rare as most of our friends houses and places we go to are within walking distance. As of July, all cars in France will need to be equipped with single-use breathalizer kits.