I actually know some guys locally who have already built a good sized wood gasifier.
So far, they have used it for running a gasoline engine (to be hooked up to a generator) and cooking bratwursts.
The main idea is to be able to scale it up to power electricity for a house, or a whole small community.
They are currently experimenting with other biomass besides wood, such as chunking up bits of left-over crops.
It's all totally renewable, and the only real "waste" is charcoal leftover from burning the wood, which can than also be used for many things, grilling food being the least among them. They also pump CO2 from the burning into the greenhouse to keep the plants happy!
EDIT: Talked to this guy last night. He and a few other fellows have been tinkering with doing this to a car. They plan to have it up and the Midwest Renewable Energy Association's Alt Car Show next summer!