So, NovaResource has provided 3 examples. They're not perfect but they are examples. One admits that it's not conclusive, and another has mixed results depending on weather. The remaining one was on a Prius; I would not expect Prius data to apply to other vehicles.
How about the other side? Who can provide 3 imperfect examples of WAI being effective? I know I've seen many people post that it worked for them, but looking at a few gaslogs, it's not as clear as I remember.
Here's a google search of our own gaslogs:
http://www.google.com/search?q=site:...log+wai+OR+hai
Here's the "top 100" lists from our gaslogs:
http://www.gassavers.org/garage/viewall/epa (Top 100 improvements over EPA estimates)
http://www.gassavers.org/garage/viewall/mpg (Top 100 actual MPG)