If this has been mentioned before--sorry, I  missed it.  I just heard
a
discussion on the news this evening re BioPerformance Fuel - a pill
you drop
in your gas tank for better mileage.  Sounds like snake oil to me.
Anyone
tried this?

yeah, but we called them 'mothballs'. :)
no really. the naphta or whatever that's in mothballs boosts the
octane a mite.
old trick from back in the 40's. trouble is, you put too much in
there, and you
can burn a piston. :(  not really worth the effort.
http://www.newton.dep.anl.gov/askasci/chem00/chem00485.htm
a different view ...
http://www.georgenitta.com/mothballs/mothballs.htm

me, personally, i wouldn't try it. i dimly recall someone in high
school who lunched his engine after dumping a box of moth balls into
his gas tank. now, whether it was the moth balls that did it, i can't
say. after all, it was kinda an old car. but very shortly after he put
the moth balls into the tank, he was walking to school. :)

good luck!
joel