I have just recently finished data collection on a study on HHO fuel cells and their benifits. The data showed exactly what I had expected, increased mileage. After having a talk with one of my cycling buddies, I came to the conclusion that no matter how efficient these things are, no matter the benifits, the average user will find it to complex.
HHO system designers shouldn't focus on maxing efficiency, but making it easy for a consumer. Could an ordinary work-overloaded middle class guy install an EFIE and build a dry cell? Probably, but will he want to. Hell, most people wouldn't know how to mix their electrolyte or find distilled water.
How can this problem be solved? The technology is here, and proven. How can the average, everyday, housewife for instance, use HHO? Basically, how can this stuff be commercialized and made idiot proof.
Essentially, how can we make HHO into an Apple product? One button, simple, and easy to use. (please no Apple/PC/Linux wars) I guess the goal should be making HHO accessible to your grandparents.