England and Wales
As a police officer who has in the past 24 hours carried out station procedures (where you blow on the machine costing several thousand pounds) for two drink drivers (the last one was two hours ago, she is still in a cell sobering up), I can safely say that if you drink drive then you're an idiot and you deserve to get caught.
Almost everyone I encounter is so pissed they should have known better. The limit is 35 microgrammes in 100 millilitres of breath in England and Wales. I have no idea what that equates to in American BAC numbers unfortunately but that is not an insignificant amount of alcohol. For most it's more than 'one too many', it's probably three or more alcoholic drinks. NB. if you do not tolerate alcohol well then even one strong alcoholic drink may take you over but for most the above holds true.
Those who we catch routinely blow double or more (both tests were 100 or more). That equates to a very boozy night out. But even those who blow lower stand out like sore thumbs in terms of their driving abilities - they travel too slowly, too quickly, fail to stop for traffic signals, indicate pointlessly, brake pointlessly, cannot keep in lane on any kind of bend and not to mention that even one or two drinks will leave a smell of intoxicants on you for hours. They also have a tendency to panic when a police car pulls behind them.
Here, the police need a reason to breathalyse you (if you have a crash, if you break the traffic law or if the officer suspects you have alcohol on you) but they can stop any car for any reason. This means they can stop you and see if there are grounds to breathalyse you but it's not an automatic right. This is what the police do routinely in the summer and during their Christmas drink drive campaigns and as a result of them, they catch loads of people out. The officers who decide which cars to stop are incredibly good at it and often get results, even on the 'morning after'.
The morning after is tricky but you are all adults. If you're hanging out of your arse, you're unlikely to be fit by any stretch of the imagination but a rule of thumb is one drink (normal beer not double shots etc - call them two drinks) per hour AFTER you've stopped drinking. So if you've had eight bottles of beer and finish drinking at 2AM, go nowhere near a car until at least 10AM. Your mileage will vary significantly depending on what you've drank over what period and on other factors such as stomach contents, build, metabolism, genetics, sleep etc. If you pass out, alcohol in your stomach may continue to be absorbed into your blood after you wake up. My own rule is that I will never drink until after lunch after any kind of night at the pub. If it's anything heavier, I skip driving for the day.
Most are not happy at getting caught drink driving but the fact is if you do it, you've only got yourself to blame and there is very little way out of the charges. The procedure is agreed nationally and has survived hundreds of appeals and loopholes, the machines have been proven reliable and accurate and most officers are incredibly good at following the procedure. Only if you're borderline do you have any hope of getting out of it (blood test being lost, coming back negative etc).
I think it is absolutely right that drink drivers lose their licence for 18 months or more and get fined. It's definitely right that repeat offenders go to prison. Far too many accidents and fatalities occur due to drink drivers.
For reference the police use devices such as those from Drager (costing over £700 each) for roadside tests. In my experience the results tend to be within ±10% of what the station machine reads. The boxes are calibrated monthly and are extremely reliable. I for one would not rely on one of the devices reviewed nor any kind of disposable test! If I had any doubt, I wouldn't drive but if I wanted such a device, there is no way I'd waste £100-200 on one of these, I'd shell out for something Home Office approved.