Proven to work remarkably well but I didn't see much discussion on its use.
There are drawbacks:
It pisses some truckers off.
You have to be hyper alert because room for reaction is minimal.
In high ambient heat + long duration situations, the reduction of airflow over the radiator can lead to increased operating temperatures.
Legality varies from state to state (tailgating type of laws).
i've been toying with this a little bit, mainly on my long uphill drive home. Almost always trucks in the evening (making runs to Arizona). Of course, being a 91, my truck can't be monitored for mpg's at a specific time, but i'll be darned if i don't have to back off the throttle once i get into the 'sweet spot'
I have noticed that the trucks don't seem to like it though, not sure why really, wonder if i actually can hide myself completely behind some of them. he he.
Also, seems to work best on square trucks, not the kind that haul sand/rocks etc.