It has been said on these pages before that it is not advisable to buy a diesel with a DPF if you do short distance trips. This obviously does not help johns159 though - sorry.
Perhaps manufacturers should be a little more upfront on this - we know it is not just Alfa that has this issue.
My 159 1.9D has now done 40,000+ miles, with no issues whatsoever, so it can be done.
I was a little wary of taking the car to Scotland this summer, with a trailer on the back, (limited to 60mph ish), as I thought cruising at about 1800 rpm for 600 miles would cause problems, but it was fine.