PolygamousRanchKid sends this excerpt from El Reg:
"The U.S. Air Force's second mysterious mini-space shuttle, the X-37B, could be spying on China's space laboratory and the first piece of its space station, Tiangong-1. Amateur space trackers told the British Interplanetary Society publication Spaceflight that the black-funded spaceplane seemed to be orbiting the Earth in tandem with Tiangong-1, or the Heavenly Palace, leading the magazine to speculate that its unknown mission is to spy on [the lab]. ... The lab is unmanned for the moment, so all there'd be to study is the technology of the craft and what experiments it's doing. Still, the U.S. is hugely suspicious of China's space endeavors, so it's more than possible that they'd want to get a look at Tiangong-1 just in case it's doing anything unexpected."
Update: 01/06 21:50 GMT
: Further calculations have shown that this is not the case