There has been quite a bit of investment and research into methane from landfill, in Australia. This is one report that has mixed views on this process.
Like all technologies, the methods of capture and the efficiency of this source of energy, is continuing to get better. Landfill is a poor way of disposing of human generated waste, but at least using what would have gone into the atmosphere (methan gas), will at least mitigate some of the problems of this kind of waste disposal.