Just real quick this isn't a scam. I own a 93 toyota pich-up truck with a 22RE engine which before I installed my cell got around 17 to 20 MPG. Now with my cell installed I get 30 to 35 MPG. So I say it isn't a scam. I'm still tinkering and adjusting my system ie. Power module and o2 sensor cheater. I have plans on buying a high output altenator and building a second cell. I'm running a tero cell or some call it a dry cell that are 80 to 90 percent efficent, which is better than the mason jar types. Also to those concerned about water use I average about 4 oz of water to 100 miles. I haven't had any problems with it. I found a guy on you tube that runs a 3.5 horse generator on hho alone. link to that said video
http://www.youtube.com/watch?v=va2azUA8kaE Its a little long but watch it its pretty sweet. here is a link to the plans I used for mine, I did however do some things different.
http://www.umpquaenergy.com/hydrogengenerator/tero_cell.pdf
So thats what I have to say about all of this. By the way you can get a tax credit for alternative fuel for you federal income taxes. I haven't got to reasearch this part yet but I will soon need to get on that. Hope this was helpfull.