Steve, I'm looking into bio-diesel also, since there's a local source here in California.

There are some issues though, the main one is that bio-diesel damages rubber and other elastomers. It's a pretty strong solvent, it even can damage your paint. Running bio-diesel blends, such as B20 (20% bio, 80% petro) will reduce the damage, but it still happens to a lesser extent. The use of pure bio-diesel would require the replacement of all rubber in the fuel system.
Some places of concern: Fuel lines, seals and gaskets, and injector O-rings.

The other issue is whether it will void Ford's warranty.

I have contacted Ford regarding the warranty and other technical issues, and when I hear from them I'll post the info.

-Lee