A robotic insect, similar in size and weight to a wasp or hornet, has successfully taken flight at Harvard University (article and photo at MIT Technology Review). This is an amazing breakthrough, because just a couple of years ago, such robots were pigeon-sized, and thus far less useful for detailed military and police surveillance.
At the moment, the flight path is still only vertical, and the power source is external. Further advances in the carbon polymer materials used in this robot will reduce weight further, enabling greater flight capabilities. Additional robotics advances will reduce size down to housefly or even mosquito dimensions. Technological improvements in batteries will provide on-board power with enough flight time to be useful. All of this will take 5-8 years to accomplish. After that, it may take another 3 years to achieve the capabilities for mass-production. Even then, the price may be greater than $10,000 per units.
Needless to say, by 2017-2020, this may be a very important military technology, where thousands of such insects are released across a country or region known to contain terrorists. They could land on branches, light fixtures, and window panes, sending information to one another as well as to military intelligence. Further into the future, if these are ever available for private use, than that could become quite complicated.