they converted a 2.5 pd tdi taureg (how ever you spell it), a guy also converted his 2004 plate jetta but said to watch out for the egr valve as it needs to be checked/ maintained as he found out at 30k miles. to be honest thats around the same milage i started to have problems with my egr valve and i was running normal diesel. way i see it is that egr isnt a good thing for me or my car, so mines unplugged and the pipe blocked with a screw bit !
VW cant even make up their mind with regards to bio diesel blends etc either, my manual clearly states i can use a RME (rapeseed meth something mix) at a 50/50 ratio, but then change their statements to say NO bio diesel at all. then recently claim its ok to put in 5% biodiesel - do they have a choice really as most resellers automatically include 5% in practically all their fuel?
i've spent ages looking into it was what we pay for fuel is just stupidly high now, another interesting site to look at is
http://www.ravenfamily.org/andyg/vegoil.htm
and
http://www.veggiepower.org.uk/vegoilcar.htm
what ive read is that if you run higher mixes then there is going to be more pressure on the injectors as they have to work harder (especially if you mix just veg oil straight into the tank)
either way it might be worth considering / experimenting with especially if the government dont want to know for quantities less than 2500 a year
forgot to mention that the seat manuel states bio diesel doesnt offer the full performance, but gives you more MPG ? other websites/forums state there isnt much difference in performance, might be worth just whacking in one of those one shot injector cleaners from redex only 99p anyway!