I thought that you might find my experience to be a vaguely interesting contribution to the DPF discussion. I agree that, on the whole, they are probably an expensive invention of the Devil but sometimes they are not too bad. I have a nine-and-a-half years old Citroen C5 estate that I bought as an ex-demonstrator at six months old. It has the 2.2-litre engine, so I guess that makes it a first-generation FAP, and uses the EOLYS liquid catalyst system. I have only just had to replace the particulate filter (and refill the EOLYS tank for the second time), after 92,000 miles. Of course, the cost of two fills of EOLYS plus the filter adds up over those miles and makes it disappointing to see buses and lorries belching smoke with impunity - but the FAP system has at least worked well for a long time. A related point that you might want to pass on to enquirers is that a partly-blocked DPF on this car gives an 'Unblock Diesel Filter' message on the information display, which is a bit misleading because (at least to my way of thinking) the diesel filter is the thing in the fuel feed that keeps dirt and water out of the injectors.