Why is it that when I'm reading this, I keep hearing Don West's voice in the
background...  "LIMITED edition, people!!  LIMITED edition!  I'll even throw
in a McGwire rookie card.  BE DIALING people!"  :)

What's next?  A bunch of lemons, some copper and zinc probes, and a spool of
wire?  "Cut your household electric bill in half!  Get your electric company
to send YOU a check every month!.  Of course, individual results will vary"

It might get a second glance at a junior high science fair, but as a
practical supplement to gasoline for an automobile engine?  Hardly...

One year for Christmas; someone gave me popcorn that came in a
can just like that one.

My wild guess here (the website does not provide any description!) is that
hydrogen is generated via electrolysis, and then fed into engine via air
intake. This is similar to what propane-powered engine would do, and primary
danger in such a setup is that explosive hydrogne/air mixture inside intake
manifold can self-ignite and at the very least blow your intake pipe (which
is plastic). You also risk damaging MAP/MAF sensor, and if your intake
manifold is plastic then it gets blown away, too.

Secondly, fundamental laws of physics will prohibit you from any
MPG-increase here... hydrogen is generated using electricity, which in turn
is generated by alternator, which is powered by good ole' gasoline engine.
If anything your MPG will go down as hydrogen production is not lossless,
there can be leaks, etc.

Third, ECM will probably get confused by an overly rich mixture and whole
engine management can go haywire. Not to mention possible damage by water
vapour.

What did they say?... there is a sucker born every free lunch or so? ;)

Peter