I used biodiesel made from soy oil for the circumnavigation I did in a RIB a few years ago. I used 100% for nearly all the 35k miles, mixing with conventional diesel rarely (when someone "misplaced" the fuel). It doesn't smoke, doesn't stink, is good for your hands, ensures a clean and odor free bilge, and the exhaust smells like cooking oil - because it is. The cetane rating and lubricity are both higher than petroleum diesel, particulate emissions are reduced by 30% or more, its biodegradable, renewable, and is really a pleasant change from working with diesel fumes over the transom. It can be used in any diesel engine without modification and can be splashed blended with whatever is in your tank, in any proportion. That's not true, of course, of raw vegetable oil - the fats will eventually cause problems if not treated in some way.
In the US its manufactured from both raw seed and from used oil. I'm in Hawaii at the moment and there is a company here which collects the used oil, processes it, and sells it as fuel (Pacific Biodiesel). Anyone wanting further info can find it all at www.biodiesel.org
wish it was less expensive!