Robert Rapier details his visit to the Choren biomass-to-liquids plant in Germany. This basically takes waste wood, gasifies it (burns it under controlled circumstances to produce syngas (the carbon monoxide / hydrogen mix that used to be made in gas plants around the world), then uses the Fischer-Tropsch process beloved of coal-to-liquids enthusiasts to turn it into diesel. Result: diesel from trees, with carbon-neutral electricity as a byproduct. It's still small-scale, and relatively expensive, but OTOH it's a bit more flexible than standard fermentation, and it certainly beats using food.
(Hat-tip: Larvatus Prodeo)