Biodiesel is actually "cleaner" burning than most of the diesel you see rated for street use. The problem comes in the manufacturing cycles - if you're doing it at home with free, spent waste oil there isn't much environmental impact. If you're growing crops to create the oils that are turned into Biodiesel, then there's quite a bit of impact and that won't go away until efficiencies are built into the system. There's been a bit about this online but it's hard to separate the truth from the smear. If we could focus on it for a bit as an industrial nation, I'm sure an efficient, relatively "green" production method could be devised but also I'm not sure if we'll ever get to that point.

-- John