3D Traffic Reduces Traffic Congestion
If traffic management can be handled, commuters won't be stuck in a traffic jam on the interstates. If there are no pedestrians and no buildings in the aerial traffic lanes, computer control could allow much higher speed. 100 or 200 mph. That means suburbs can spread out even more, and a 200-mile commute is no worse than 20 or 30 miles today.
Flying cars might cause lower buildings.
3D Traffic Replaces Lifts
If those flying cars have smaller danger areas than present-day helicopters, it might be possible to add landing platforms halfway up a skyscraper. One of the limitations on truly tall buildings is the number of lifts, that would be solved.
Flying cars might cause higher buildings.
2D Roads into Parking Lots
Once the majority of traffic is in the air, the ground level might be converted into landing/parking spaces. That means all those commuters from the suburbs can find parking spots near their workplace.
Flying cars might replace mass transit.
An Accident Waiting to Happen
As Frostfyre pointed out, flying cars and trucks are even more dangerous than ground cars. That could lead to stronger regulation, like the computer control mentioned by User6760. You can't have an old pickup on the drive that's used every now and then to go to the hardware store. It would have to be a new and regularly maintained/certified pickup instead. If you can't afford that, tough luck.
Flying cars might require more and better mass transit.
When the cops see a broken tail light, they cannot simply stop that air car. That will deprive them of the "opportunity" to spot other suspicious things like DUI. If you believe in the broken windows theory of policing, unpunished minor crimes will lead to major crimes. If you believe that those stops are just a pretext for harassment, that will stop.
The crime rate will go up or down.
If air cars are under computer control, it becomes harder to use them as a getaway vehicle after a crime. Some criminals might reconsider their plans. On the other hand, it is pretty easy to drop a brick from a flying car. Who can prove where exactly it came from?
The crime rate will go down or up.