DPF's basically a stupid crappy naff device imposed on the public that drive diesels by someone in an office in Brussells that isn't interested in what's best, just to keep eco mentalists who can't see past the end of their noses. (Deep breath!)
Crash course, DPF catches the soot (black smoke) on a diesel and burns it off when the car is running at high speed continuously. This means there's never any black smoke, but to burn the soot off it obviously has to be very hot...in excess of 800 degrees. So if you do alot of town driving, it fills with soot and then you HAVE to go for a quick drive. Quite annoying when you're in the centre of London and it starts running rough
Mine's coming off as soon as my warranty runs out

although it is a Pre facelift.
From my research (including listening to Bigg's problems) you need someone respectable with a good track record. Andrew JB has a good Readers Ride thread detailing his experiences of de-dpf.