As Martin Kaste suggests in his article, biofuels still use nonrenewable sources in the form of soybeans, corn and other grains otherwise used for human consumption. People won't die off if we suddenly convert to biofuel, but our already overwhelming surplus of corn and soy will continue to grow if cultivated strictly for veggie oil/biofuel. Further, if the bottom line continues to churn the wheels of production, irresponsible and unsustainable farming practices will reign supreme and contribute to environmental degradation.
It's reassuring that the people of Seattle didn't commit entirely to biofuel. Biofuels can be a viable option, as long as those fuels are extracted and recycled from already used cooking oils.