It's never a good idea to drink and drive - especially if you are DUI (ie, you've drank enough to be over the legal limit (.08 in WA), or you are otherwise impaired due to the alcohol you've consumed). Many people think they will be "ok" after a few drinks because they feel as though they're in control, and will drive carefully so the officer will have no reason to stop them. The problem with that logic - in addition to the fact that alcohol can make you feel more "in control" than you really are - is that there are several reasons why an officer might make contact with you other than for careless driving (ie, traffic infraction). For example, you could be involved in an accident through no fault of your own, yet required by law to remain until police arrive. Or you could be stopped because the officer ran your license plate and your license (or that of the registered owner) is suspended.
Another reason came clear to me yesterday as I was driving through an unfamiliar part of Auburn. I was paying attention to my GPS device which told me to turn left at the upcoming intersection. As I started to, I noticed a "wrong way" sign and just beyond that, a police cruiser facing me. Had I not caught the sign, I would have followed my GPS and been pulled over. And had I been drinking, it may well have led to a DUI investigation. (Given that it was 11 am, it probably would have led to a few other conclusions as well.)
I've had at least three clients over the past several months who were stopped for following GPS directions at odds with the traffic code at that particular location. This provides no legal defense at all regarding the legality of the stop. The best policy of course remains - don't drink and drive. GPS and other faulty assumptions ("no bad driving, no reason to be pulled over") will provide small comfort if you choose to, and are pulled over.