I've heard a couple of stories of people in the states that have been fined by the sate and federal government for running on biofuel since they don't pay fuel taxes. Gotta love that mentality... Here is one story I found:

http://www.newsobserver.com/news/story/599471.html

"We have totally forgotten that a Diesel engine could run on organic matter"
We have totally forgotten what fossil fuel IS - long extinct animals.

^ getting fined for not paying the "tax" can happen in the UK too.

You have not bought the right to run your car anyway you like. You have to rent the right to run it in fuel tax...

oh, and it wont biodegrade when its been burnt as fuel.

Yeah, stick it to the oil companies by using a product which is fertilized by their products and shipped around the world via diesel-burning vehicles! That'll show em!

Uhhh... botono9, did you watch the vid? The Mercedes in the video is running on waste frying oil (chip fat) from businesses that would have thrown it away anyways. It definitely makes a difference in that you'd save 80 percent the cost than if you'd used diesel gasoline. You don't see the benefit in that?

As Issy seys, this stuff is bought, used, and then thrown away. Dumped. Filtering it and reusing it makes much more sense than binning it. It might not suit everyone, but for those with access to a free/semi free supply, it's appropriate.