"if you call a taxi, wait for it to show up, and then go into your car to get your things the police will (and have in the past) arrest you for drunk driving. " I either heard that from the driving instructor at the behind the wheel class I took when I got my license about ten years ago, or from a police officer they brought in to talk to us during that class.
My interwebs searching seems to indicate that "Most states have determined that all that is necessary to be guilty of their driving while intoxicated or driving under the influence statutes is that the vehicle be in your control, moving or not, running or not. So parked with you in the drivers seat is "operation.""
http://boards.straightdope.com/sdmb/archive/index.php/t-497814.html seems to have a few antidotes along those lines.
http://www.click2houston.com/news/21789609/detail.html Arrested while waiting for a cab, but the arrest was for public intoxication. They were outside the bar and took a cab to the bar. "A Montgomery County prosecutor said if you call a taxi after drinking alcohol, you are typically better off waiting inside the establishment instead of in the parking lot."
http://www.expertlaw.com/forums/showthread.php?t=11400&page=1 Also says the same thing, you just have to be in control of the car, not trying to drive it.
I also found a few incidents were people listening to the car's radio in their driveway with the engine off were arrested for drunk driving, even though the situation strongly indicated they had no intention to drive.