A handful of Grist readers were perturbed that our recent article on eco-friendly cars didn't mention biodiesel; writer Jim Motavalli responds by noting both the upsides and the downs of this fuel fave. Other letter writers tout the benefits of waterless urinals, talk up tankless water heaters, boost Wesley Clark, dis Dennis Kucinich, and issue a call for jocks to save the planet. Find environmental opinions galore -- on the Grist Magazine website.