[Red71gmc]

The previous poster was correct about ethonal replacing the mtbe. MTBE never breaks down in the soil so leaky ground tanks caused ground water issues. Ethonal limits our need for foriegn oil and all the politics involved in that. Ethonal is produced here in the USA and is a constant renewable resource we raise. The distilled grain after ethonal is extracted has nearly the same value for life stock feed as before. It all makes great since and yes I raise corn.
To answer the original posters question, don't use the crap in older vehicles or even new 2 strokes. If your mower has a larger more expensive engine like a Vanguard or Briggs Commercial it will be fine. If you have a low end push mower with the cheapest engine Briggs makes, don't use it. It will ruin the carb.
I also have a store and sell mowers and 2 stroke powered equipment. 80 percent of our shop repair is ethonal ruining the small cheaper carbs. We chuck the old carbs and put on new ones and warn the customer to stop using it. We can rebuild and clean the powdery residue off the carbs but it pits the low quality meatal and comes right back.
I only use non ethonal in my 71. I get 2 mpg better fuel miliage and it starts right up. On the blend it is a little more tricky starting.
If you drive you older vehicle daily or very often you may be able to get by with it. As other posters have said it attracts moisture and is corrosive to some metals. If it is not sitting in storage it would be maybe ok. For storage or sitting long times I would put non ethonal in it or at minimum use the additive previously described.
I am of course a big fan of ethonal being a corn grower. I like the fact we are more independent from foriegn countries we would other wise not like at all. I like that it is a renewable source and we are not depleting resources. I also will admit all day long it has its issues and don't use it myself in everything.