Traffic jams are real, but putting the cars in the air isn't going to fix that problem. The key problem with driving cars into cities is that they take too much space per passenger (at rush hour, on average, 1.02). Granted, putting traffic corridors in the air gives you a bit more space, but you also need to leave a lot more safety margin.
Flying in a straight line might save fuel compared to flying detours, but that doesn't mean it saves fuel compared to driving. These flying cars don't stay in the air all by themselves, you know? And, seeing as we're all bitching about the price of gas to drive... ask your friendly helicopter pilot how many gallons his chopper burns per hour.
There are solutions to traffic jams. Telecommuting, walking, cycling, public transport.
Oh yeah, and if your hearing's still too good: Suggest to Air Traffic Control that they replace the couple of hundred planes / day over, say, LAX, with a couple of hundred thousand planes^H^H^H^H^H^H"Flying Cars" per day.
Don't get me wrong, I'd love to have a flying car. But frankly I'd rather save up for a one off trip to space instead. At least I won't have to kid myself that that's solving any problems.