As far as that goes, gasoline has a few problems also...

Gasoline is extremely volatile and anthropogenic VOC emissions are the main reason why ground-level ozone (smog) persists in urban locations in the U.S.

Gasoline engines stink worse than diesel after cold starts (in my opinion).

Diesel fuel is currently more expensive than gasoline but it appears to be because of a supply and demand issue, not because gasoline is fundamentally less expensive to produce than diesel fuel. As a matter of fact, diesel fuel requires much less energy to refine than gasoline (also a CO2 emissions issue). At least two refineries have announced plans to increase diesel fuel output relative to gasoline, so there may be less of a supply/demand issue within the next few years (the relative amounts of gasoline:diesel refined from a barrel of crude oil is actually quite flexible).

Regarding the cost premium of a diesel hybrid, Ricardo has demonstrated that they can reduce the premium (over gasoline hybrids) to about $1000 ( http://www.dieselforecast.com/Articl...?articleID=321 ). Not sure if emissions equipment is factored into this, but it should be easier to meet emission regs with diesel hybrids anyway since most NOx emissions with diesel occur during power transitions, and hybrids smooth out the transitions.