Cant say i'd want to use the soap, it doesnt look or feel very appealing!

I have used it MB, and our car runs really well on it. Runs smoother, quieter and the fumes smell much nicer! It's supposed to be much better to run as being more oily that your regular diesel, it lubricates the fuel pump and wotnot. In small quantities, it costs around 60c per litre to make, but if you started making larger batches on a regular basis, it can get as cheap as 35-40c per litre. If you have a methanol recovery system, cheaper still! Diesel at the pumps is currently $1.03 per litre.

I dont think I'd use my own brand fuel on a new car with sophisticated injection systems though. It may well work, but being thicker than petro-diesel it could block something up. You also have to be careful with what your fuel lines are made of, as it's slightly corrosive to certain materials, so can rot your fuel lines, causing them to 'weep'. I think I read somewhere that the majority of cars made after 1990 had fuel lines that could carry biodiesel. On the flip side of that, it also removes the build up of crap that regular diesel creates, so improves the performance of the car. You have to change your fuel filter a few times to start with as they block up frequently with the gunk it removes.

I ramble on sometimes....