We've seen lamps that run on human blood and examined robots that eat corpses for fuel. Sweden is already using flesh-based biofuel, but it's not humans they're using to heat their homes; it's rabbits.
Why rabbits? The fuzzy critters have actually become a bit of a pest in Sweden; wild and stray pet rabbits alike have ravaged city parks in Stockholm, forcing hunters to think out the population. With all those bunny bodies piling up, it makes sense to put them to good use. So the bodies are shipped to Konvex, a company that turns animal and vegetable oils into automotive and heating oils. But even the reproductively prolific rabbits don't provide sufficient power, so Stockholm supplements their bunny-based power with other animal corpses, including cats and horses.
So does this mean human-derived fuels are next? As Scientific American notes, the jokes have been made. A group of activists called the Yes Men crashed a gas and oil industry luncheon, claiming to be representatives from Exxon Mobile. They then proceeded to deliver a presentation for a mock product called "Vivoleum," a fuel made from human bodies. The audience was reportedly less than amused.
Burning bunnies for biofuel? [Scientific American]