Chicago Trib story on the increasing value of yellow grease.

It's a great idea to convert used fryer oil to biodiesel.  But understand this, there isn't enough to supply the entire driving population.

I'm a bigger fan of using the biodiesel in maritime use.  It reduces the impact of the ports/harbors.  But that's not the main problem.  The big problem for the converters is getting the feedstock.  And odds are, it will be local government, not the free market that will determine where the yellow grease goes to.