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.
Sounds like what I've read on other sites. Most responses said the jets needed to be about 20% larger. Seals and gaskets also need to be upgraded as you said. The only other problem I've read about is water in the tank, since its nearly impossible to get all the water out of ethanol. This becomes a problem only when switching back to gasoline. And yes, my interest lies in producing my own fuel since a have a small farm and can grow my own supply! Thanks for your response.
I have been running my 782 Cub Cadet with a Vtwin Kohler on E85 for two years. I have the carb as rich as possible and pull the choke out for colder seasons. It starts a bit hard, but once it's running, it's fine.