So let me just start by saying that absolutely in no case is it ever OK to drive a motor vehicle while intoxicated. Unfortunately however, just about every state in the US has laws on the books that charge you with a DUI if you DON'T drive your car, but are merely attempting to use it as shelter while waiting to sober up.
A common example of this might be that you are out one night, things get away from you a little bit, and as the bar empties out, you realize that while you're not completely hammered, you're still past the threshold of being ok to drive. So you get in your car and tilt your seat back to sleep it off in between sips from your bottle of water. Next thing you know, you're awakened by a tap on the window, and a cop takes you in for DUI, despite never actually having driven.
Often times, the difference between a conviction and not in these cases is the location of your keys when the officer finds you. If your keys are in the ignition or the engine is running (even just for heat on a freezing night), you're almost certain of a DUI. However, folks who put their keys on the passenger seat or elsewhere have had luck getting their cases overturned. Google "actual physical control" for examples.
"Key in the ignition" does not apply to Volt owners, as our "keys" work from anywhere in the vehicle. Would we have to chuck them a few meters outside of the car to stand a chance? What if we use the smartphone app to turn on the A/C or heater, making the car technically running, but not drivable?
Any cops/lawyers have any idea? Again, not that I'm planning on doing this anytime soon (nor is this a problem I'm facing right now, if that's what you're thinking, haha), but I'm willing to bet that as "smart keys" and iPhone apps that can start your car's accessories become more widespread, that something like this will matter a lot more to people who were otherwise trying to do the right thing.