So they're either (a) blindly throwing aerodynamic darts, hoping some of them work; or, (b) doing it for the "neat-o" factor.
I'm betting on the "neat-o" factor...
You'll be hard pressed to find empirical evidence showing fuel saving capabilities on passenger vehicles.
I tend to agree.... But I stand by my previous comments - that the concept is sound. The implementation, of course, is where things become questionable - so far, we can be certain nature is the closest to a good implementation I will hopefully have some CFD in the next few weeks to bring some non real world data to the table
Time is the best teacher. Unfortunately it kills all its students.