There have been a number of flying cars over the years, such as the Model 59H AirGeep II. They're just expensive and impractical, so nobody ever builds more than a handful of them.
I never thought the "flying" part was the core technology... it seemed to be the invention some non-traditional, low-noise, propulsion & power source that could levitate heavy objects. I don't think we have that ... if we did, the expensive and practical part might be solved and we'd have them everywhere :)