I have heard that the new gee wizzz turbo diesels are going to be arriving this year. This will be bad news for the hybrids.
lazs
Diesels might save the truck and large SUV market - particularly if you do a lot of heavy towing where a diesels will murder a gas engine for mpg. For the light truck and car market, the economics are less clear cut.
Let's say you pay $4000 premium to buy a diesel Honda Accord over the equivalent I4 gas model (heavier engine construction required by higher compression / expensive exhaust cleaning systems). Let's also say that diesel retains its 20% cost premium over regular gas - say $4.80 versus $4.00 a gallon. Now let's assume the gas car does on overall 26 mpg to the diesels 40mpg. That gives a cost per mile (for fuel) of 15.4 cents per mile for the gas car and 12 cents per mile for the diesel.
To recover that $4000 initial outlay, you're going to have to cover 117647 miles. Bear in mind diesels also tend to have higher maintenance costs. There's also the question of where the additional diesel comes from if demand goes up. Its not like there's huge amounts of spare gas refining capacity that could be converted, and the process is apparently pretty expensive.
Of course, there are other factors to consider not least of which will be that the diesel will probably be a far nicer car to drive than the gas model with freight train like torque for overtaking and relaxed low-rev cruising. I drove the previous generation European Accord with a diesel engine (Acura TSX in the US market) and it was a really nice car. Buy it as an alternative to a V6 and it makes a bit more sense.
All in all though, gas engine technology is moving ahead as well and I think for the time being, gas is going to rule the US market.