In the USA, the FAA has a voluntary standard for model aircraft that limits operation to 400 feet AGL.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/1acfc3f689769a56862569e70077c9cc/$FILE/ATTBJMAC/ac91-57.pdf

The new legislation for UAVs picks up that 400 AGL limit as I recall.

That said, there are pirates flying quadcopters much higher (7000 meters?). Search Youtube for 'quadcopter altitude record'.