I have been making & using Biodiesel for about a year now. I use my B100 in my Pug 406 2.1tdi. Done about 15000 miles now.
There are loads of forums about the making and using of BD. You will find all you need to know about it in them.
I pay my tax as I am a licenced producer, and it works out about 36p/l tax paid.
I bought an Allroad 2.5tdi yesterday.. As yet I have not used my BD in it, but am told it should be fine.
I did see in one thread that people were having trouble with B100. On the course I went on I was told to introduce BD in stages to get to B100. BD is a very good solvent, and in the first 1-3000 miles it will clear ALL the sh*t out of your fuel tank and system. If you want to know more about BD, I'll be happy to answer what I can.
Oh! did I mention I make the equipment to make BD :-)