A lot of the anti-fracking controversy has focused on the potential of unburned or escaping methane to harm the environment through increasing atmospheric warming.
Here is a link to research on a new catalyst that uses nanotechnology to burn methane without methane residue: it is 30 times more effective than current catalysts.
http://www.sciencedaily.com/releases/2012/08/120809141619.htm
This could have profound consequences for the efficiency of natural gas as a fuel.