Update: Well, clearly this was already being done when I asked for it, just not at the airports I flew from. It's now close to universal.
Airport pickup is becoming another nightmare in some cities, with police barring cars from waiting for passengers, causing people to circle.
Airports should take a piece of parking lot and turn it into a marshalling area for people with cell phones. If you are picking somebody up, and you have a cell phone, you go to the marshalling area, where cars wait in parked lines like a parking lot. When you get a call from your passenger saying they have bags and are ready to go to the curb, then you go out and get into a special passenger pickup lane. You go right to the numbered spot your passenger told you. For passengers without cell phones, phone booths will sit at the exits of course.
For those not with cell phones, there is of course short term parking or the endless circling, though generally you want less of that.