That's it doing a regen. 500 miles or so is normal too....
Yep, Sounds perfectly normal.
However if you are stopping the car or driving in traffic whilst it's trying to regen then it won;t be completing it.
I would recommend going for a long drive one weekend, get on the motorway or a local dual carriageway and do 100+miles (Take the Mrs for a day out at the beach or whatever is convenient)
In the later cars (I only noticed this in my current 2.0JTDm) if the DPF is really blocked you get a warning on the dash when it's regening (not every time, only when it's bad) My previous 1.9 never warned me, it just got crappy MPG and bad performance.
The turbo gauge dropping to zero very quickly when you take your foot off the gas is the tell tale sign that a regen is happening, this will also tie in with massively reduced MPG on the trip computer on the dash. If you notice it happening then best to keep driving for another 10 mins to let it finish (especially if you are on the motorway, just carry on to the next junction if you were about to come off)
I have a rubbish routine which involves 7 months with 250 mile trips every weekend where the DPF stays in god condition and I get good MPG followed by 5 months of pottering around town doing no more than 10 mile journeys in heavy traffic, 3 months in My MPG drops by at least 10mpg around town and the DPF warning light comes on. So I go for a long trip at weekend and all is good again.
Not a blast, just drive normally on a motorway for a long way will sort it out, It doesn't need an Italian tune up, just a chance to burn off some soot.
I have a colleague (who only does the pottering around town type driving) with a 1.6D VW Golf and his DPF warning light came on, I advised him to do a trip round the M60 (33miles all motorway) and sure enough the light went out and his performance/economy returned. DPF equipped cars need a descent run every now and again to clean out all the crap regardless of the make.