Lots of new info flowing on the Internet these days about biogas and methane digesters. Here is a recent post form John Robb at Resilient Communities about using biogas for increasing one's resiliency.
And here is a DIY tutorial I came across on how to build your own small-scale digester.
A summer project I have lined up is to build a digester and then try to connect it to a small propane-powered refrigerator. It would be a wonderful addition for grid-down situations.