Current diesels, having owned a Golf and now a Beetle convertible with one, are very clean, still efficient, and even fairly quiet. You could sit behind my car when I start it or its running and not detect a scent of diesel. In fact it can be less offensive than some gasoline cars.
Still I drive in a world of public buses and commercial dump trucks that just pump plumes of black stuff into the air. Makes it hard to sell to the average consumer.
That is changing, besides VW, Audi, BMW, Mercedes, and Porsche (see the pattern), Jeep will have a Grand Cherokee with a diesel, Chevrolet has a diesel version of the Cruze, and Mazda will have a 6 with one as well.
In my case I wanted a fun to drive car, its a convertible, that got very good mileage. All the hybrids to me are penalty boxes. So when I saw VW was going to offer a convertible with the efficiency that a diesel belongs I jumped at it.
I don't think the price of diesel is coming down in the USA relative to gasoline. The USA already uses lots of diesel in its trucking networks; switch the entire public to diesel and it's only getting more expensive.
In Europe, diesel is usually cheaper than petrol though the reverse is true in the US. From what I saw last December, price differences of $0.50/gallon weren't very unusual. If the price comes down, I think diesel would quickly become a no-brainer decision for car buyers.