Human feces is not "really hazardous stuff". There are certain things to be careful of like anything in life. I've composted my family's "waste" and used on our garden multiple times following the method in Humanure, written by Joseph Jenkins. When properly composted there is no problem. I've even done it in the suburbs and it works great. It fits into permaculture's value/ethics system perfectly. I've also visited a dairy farm in VT that powered the farm and 3 other households using farm produced methane. They were not compressing it for car use though. I just wanted to contribute some more positive info about composting human feces as it is a valuable resource and should be treated as such, bearing in mind the correct methods of composting and handling.
Loads of good info here on compressing methane: http://cr4.globalspec.com/thread/14709