The B&S go kart guys have been doing it for years, you have to open up the carb jetting something like 3 times larger, and in some applications, gaskets and rubber have to be upgraded. I guess the main reason is that it runs cooler, and I think a higher compression ratio can be used without fear of detonation. But for regular use in a lawnmower or such, the modifications needed may not be worth the trouble, unless you have your own still! Is that why you are wondering???
I messed around with some E85 in a Stihl FS 80, and after adjusting the carb wide open, I could get it to run, but the RPM was very erratic, performance wasn't very good, which is partly because I didn't really have it tuned right, and alcohol has less BTU's than gas, so you end up with less power. I let it sit for about a month with a 1/4 tank of this stuff in it, and it slimed the tank, gummed the filter, and ruined the carb. A lot of pieces and parts have to be hardened and upgraded to make it work.