This is one of the most interesting threads I have seen anywhere recently - so much so I sorted by date and went through again. It is great to learn so much about day-to-day use of hybrids and about batteries and diesel technology.
One thing which is not clear is whether diesel is inherently more expensive to produce than petrol. I suppose the differential depends, in part, on the type of crude and, possibly, dealing with sulphur.
The free gift of hybrids is regenerative braking - the fossil fuels we will continue to waste until this is universal should make us weep.
The thread contains convincing evidence that there is no real barrier to diesel hybrids. My arithmetic suggests that a diesel-powered Prius would do around 35.
What remains unresolved, for me anyway, is whether there is (or needs to be) any significant difference in pollution between petrol/diesel.