I was reading through Honda's press kit again and noticed this time a paragraph on aerodynamics. They claim the Insight has "the best aerodynamic performance in its class," but I wonder which class? It also says the Insight has "the flattest underbody of any Honda production vehicle." Here's a CFD image:
Profile:
The underside is particularly interesting since the regular Civic on which this is based has no diffuser panel under the trunk, in any variant.