Another discussion mentions a recall in which there is a software change to the regeneration program for the particle filter
http://www.volvoforums.org.uk/showthread.php?t=95323. Has your vehicle been recalled? If not, you should ask the dealer about this.
As I understand it the main point of this recall is rise in the engine oil level due to diesel fuel getting into the oil, but even if you have not had a rise in oil level it's possible that the revised regeneration program may be a benefit to the problem the DPF getting sooted up when it is driven on a lot of short trips.