Power kites are generally used in conjunction with a vehicle, such as in kite surfing (on a surfboard), kite buggying (on a purpose-built 3-wheeled cart), kite skating (on a skateboard or roller skates), or even kite skiing (on, of course, skis). Also somewhat popular is kite jumping, using a power kite to pull the jumper tens of feet above the ground in a controlled leap.
Kites of related design are used for sailing, including speed sailing. The world record in the early 80's was reportedly held by a kite-powered boat.
WARNING! Powerkites can be DANGEROUS! Lightweight people can easily be carried off, and dashed against water, buildings, terrain and power lines! Even in water, a helmet is recommended when flying a power kite, because a gust can (theoretically) carry one over the beach. On land, serious power jumpers use a full set of pads as well.