Boy the speculation sure goes crazy
Ok guys. First of all on the petro diesel fuel. Sulfur IS NOT a lubricant and does not provide lubricity. People started thinking this when low sulfur diesel came out and it had low lubricity. Its not the lack of the sulfur that causes the drop in lubricity, it's the process that removes the sulfur that also strips lubricity from it. Sulfur is what causes soot when burned and our current (500ppm limit) crappy quality diesel fuel is the reason we cant import a lot of cooler diesels, the high sulfur makes them fail emissions testing. Most of Europe burns ULSD(ultra low sulfur diesel) which is around 15ppm sulfur. Most of the US will be switching to this in 2006.
I've run b20 in my E300 for 2 years now, and have run b100 in my TDI for 20K miles. First of all , coachgeo is incorrect in his speculation about fuel filter changes. Sure, some folks that have a few hundred thousand miles and have a lot of gunk in their tank may have to change their fuel filter once if it clogs(although I've not heard of a single one yet, except from folks that homebrewed). Biodiesel is a great solvent, and has incredibly high lubricity. It also usually has a higher cetane number, which helps it burn more completely and quickly. The only downsides to b100 is that biodiesel has slightly less BTU's than normal diesel, so you will experience maybe a 5% mpg and power loss. It's worth it for the great smell, and smooth quiet performance.
If you're running an older vehicle, be prepared to upgrade your fuel lines. The best material to use that's compatible with biodiesel is Viton.
Last word of caution - be sure to wipe off any biodiesel you spill on painted surfaces, it will eat thru it, due to strong solvency. Also biodiesel is great to soak sooty parts in etc, for cleaning purposes.
For all you guys reading up on it and thinking about trying biodiesel, do it, you'll love the better smell, less smoke, quieter and smoother operation, and knowing some of your fuel dollars went to american farmers, not the middle east. Trying b20 is no risk whatsoever, and requires no mods. You will notice smoother and quieter running on b20 with about no power loss.