Well personally (I know I may seem a bit of a Kiljoy here) I think the drink drive limit should 0!
Okay, there should be some leeway incase of false readings/nautural alcahol, but I dont think anyone should drive after a drink.
It does not matter how much drink you have, even at the limit your reaction times and alertness will be reduced, as will your capability to drive.
Should be zero tolerance on drink drivers, I heard somewhere once that drivers who are under the limit, but have had a drink, make up for around 30% of accidents, although they can't all be directly related to drink.
If someone being under the limit, takes one life as a result of their drinking impairing thier ability to drive, thats one life too many in my opinion.