Having glanced over the above posts I kind of agree with what everyone is saying.
DPFs are only effective when they're hot, about like CAT converters in cars are at their most efficient when hot. When they get hot enough it allows them to burn off the carbon deposits much more effectively and stops them getting so clogged. The engine will also run much cleaner when it is hot, which helps prevent the problem also.
That said, I drive my car to work and back every day, it is about 3 miles, the temp gauge is barely off the bottom of the dial by the time I get there in this weather, so it shouldn't be doing it any good at all. Have been doing this since July and I hardly every go any distance in it - I can recall 2 journeys in here that were greater than 30 miles since July. I've never had a single issue, no warning lights, nothing.
So it prove it can do it, although I could be leaving myself open to problems later down the line who knows.
That said I do keep an eye on her and do have the software to perform a software trigger DPF regen - which is very fun to watch!
For me the biggest problem you're going to see is that round town and short journey stuff the dervs just are not that economical.
Honestly, if you want something fun to bomb about in for work, I'd be looking at one of the late 140/150bhp 1.9 JTD M-Jet 16v 156s. They don't have a DPF (EGR only), they're lighter, better on fuel and a much more sporty drive.