has anyone heard of the HHO generators, or better yet, any build one yet?

I've been doin some research about this, and basically it is a home made hydrogen generator that can be hooked into a vehicle's engine...and supposably it will help save fuel consumption...and get better gas mileage (Like 40-60% better gas mileage)

Here's a site I found: http://h2o.localal.com/

LMK what you guys think...Because I'm interested if this can really save me from gas consumption money....