For the last decade, the U.S. Air Force has been developing and launching lightweight (under half a ton) reconnaissance satellites. This is the TacSat series. The first one was launched six years ago, while TacSat3 went up last year, and is now delivering data to combat commanders in Afghanistan.
TacSat is not alone up there. There are a number of lightweight photo satellites in use. Two years before the 109 kg/240 pound TacSat 1 went up, Israel launched the 300 kg/660 pound Ofek-5. While TacSat 1 had only an infrared camera, regular camera, (both low rez) and a radio signals collection package, Ofek 5 a had one meter resolution digital camera, good enough to tell the difference between a tank and a car and spot a group of tanks assembling for attack.
The 400 kg/882 pound TacSat 3 had a wider array of sensors, including a hyperspectral (can detect a large range of light sources) imager, an Ocean Data Telemetry Microsatellite Link and the Space Avionics experiment. TacSat 3 sensors have a four meter resolution, but the ARTEMIS hyperspectral sensor can detect vehicles hidden in forests, as well as buried roadside bombs.
The problem with these microsatellites is cost. The cheapest way to launch these small birds is via a solid fuel ICBM (preferably one that is being retired). Even there, the launch cost is going to be about $20 million per satellite. It's cheaper, and more convenient, to use larger UAVs to carry the sensors. The ten ton RQ-4 Global Hawk UAV can carry 1.2 tons of sensors, more than adequate for ARTEMIS. A RQ-4 costs $35 million, without payload (and normally over $120 million when equipped with satellite grade sensors.) The smaller, 4.7 ton, MQ-9 Reaper can carry a payload of 1.7 tons, and costs less than half as much as the RQ-4.