Stumbled on this interesting article:
http://www.evworld.com/view.cfm?section=article&storyid=807
The author argues that diesel-hybrid vehicles are not feasible, apparently because the benefits don't significantly outweigh what you can already get from gas hybrids. I think his argument is flawed because he bases his case on the Benz E-class platform, a heavy beast. He also doesn't consider the benefits of operating a diesel hybrid on biodiesel. I think a smaller, lighter diesel hybrid that's more affordable to average folks (i.e. in line with the Toyota Prius) would be a hit.