"The emergence of U.S. shale gas resources to economic viability affects the nation’s energy outlook and the expected role of natural gas in climate policy. Even in the face of the current shale gas boom, however, questions are raised about both the economics of this industry and the wisdom of basing future environmental policy on projections of large shale gas supplies."  

This new report from the MIT Joint Program on the Science and Policy of Global Change has a good overview of chances and risks of shale gas production.