http://en.wikipedia.org/wiki/AdBlue
Merc service manager told me the Adblue thing requires a full flush as well as replenishment at each service and that this was a very expensive additional procedure.
With small direct injection petrol engines becoming more and more efficient, (e.g. the new BMW328 twin-scoll turbo 2.0 petrol buring just 6.3 L/100 km's while still providing strong performance), when you factor in the extra regular service costs associated with a diesel and all the potential deep cycle service / replacement costs, you've got to wonder if Euro 5 and Euro 6 reg's are effectivly the nail in the coffin that ruins diesel's long held efficiency advantage ?
DPF's were widely fitted to Euro diesel's from 2007 onwards to meet Euro3 reg's so if you can find a 2006 diesel vehicle with low km's and no dpf chances are you'll pay around about 30 - 40% of the vehicles original cost and provided its been strictly maintained in accordance to the manufacturers requirements, you've got yourself something that'll probably give you less grief than a new vehicle of the same type, (i.e. a bargain).