I stick to softies if I'm driving when out. I might have a sip of someones drink if they are asking if I think it's off or something, but no more than literally a sip.
It is outlandishly irresponsible to drink and drive. I don't care for any excuse, save maybe for a life/death situation. (Which driving is anyway, but meh.)
Jez - whilst you have a point, you are either forgetting or don't know, that alcohol starts to take an effect on your reaction times and motor control much before you (or anyone) can tell they are beginning to get tipsy. When simply walking/sitting/standing after only a small amount of drink you'll not notice it. But step into a car, where you are making many more decisions and reactions, and need to make them a lot quicker - even if driving at 20mph - it can have a massive effect.
There is also the point that the first time, you are on edge because you know you are 'over the limit'; but what about the next time? Or the time after that? Still not had an accident? Bah, it'll be fine then. Best get a move on, Hollyoaks in the City starts soon, eh?
This is when it's most likely to happen, after you slip into the comfort zone and don't realise how much of an effect that nights drinks have had. Or perhaps someone pushes it a little further.. "I was absolutely fine on one last time, I'll have two this time." and so on.
Sorry if regurgetating.. when things got sour I skipped.