According to Back to the Future, these should be ready by now. In fact, we do have high-speed hovering trains, so one might think that hoverboard technology is on the horizon. Google X's researchers looked hard and long at the potential of making a skateboard that hovers above the ground. Naturally, the first problem encountered was that, in order to harness the magnetic levitation properties of bullet trains, hoverboards would need a system of magnets on the ground.
However, even this proved complicated when researchers made floors consisting of magnetic material. They found that it was pretty easy for the board to flip over, causing big balance issues. Google researchers were able to make a tiny, quarter-sized hoverboard using a thin sheet of graphite. But they have encountered serious issues scaling up the board to a size that could hold a human (even if that human had fancy, self-inflating shoes).