One of the main premises for a vacuum that can hover is to reduce the wear on tear on your carpets and floors. The vacuum cleaner rides on a cushion of air and there are no brushes to damage the floor.
One of the first hover vacuum's was the Hoover "Constellation" that first came out in 1952. You can read more about it at the Vintage Vacuum Cleaner Museum.
A modern version is the British Airrider.
We have never tried one, and we don't plan to purchase one anytime soon. The large amount of airflow required to generate lift for the vacuum would cause any loose dirt or dust to be blown around. Maybe these problems have been solved, but for now we will stick with our old model.