I've done a bit of googling on this myself, and all I can find is that evidence could be thrown out in a criminal case based entirely on aerial footage, but that is rarely the only evidence provided. You likely don't own the airspace above your property, certainly not above a thousand feet, and technically no one owns outer space, so I would say that in 2013 or beyond, your expectation of privacy in your back yard is likely to dwindle severely over time.