I looked it up and here is what the USGS says about methane hydrates on its website :
Hydrates store immense amounts of methane, with major implications for energy resources and climate, but the natural controls on hydrates and their impacts on the environment are very poorly understood.
Gas hydrates occur abundantly in nature, both in Arctic regions and in marine sediments. Gas hydrate is a crystalline solid consisting of gas molecules, usually methane, each surrounded by a cage of water molecules. It looks very much like water ice. Methane hydrate is stable in ocean floor sediments at water depths greater than 300 meters, and where it occurs, it is known to cement loose sediments in a surface layer several hundred meters thick.
The worldwide amounts of carbon bound in gas hydrates is conservatively estimated to total twice the amount of carbon to be found in all known fossil fuels on Earth.
This estimate is made with minimal information from U.S. Geological Survey (USGS) and other studies. Extraction of methane from hydrates could provide an enormous energy and petroleum feedstock resource. Additionally, conventional gas resources appear to be trapped beneath methane hydrate layers in ocean sediments.
So from what I'm seeing from a quick overview of the subject, it seems that methane hydrates are seen as a possible source of energy (although there is some debate concerning the economic feasability of exploiting such a resource) and as a devastatingly powerful source of greenhouse gas. See also this 2005 article, "US in race to unlock new energy source" , as well as this Wikipedia entry for more info.