http://www.msnbc.msn.com/id/25936782/ns/business-consumer_news/
Theres a few articles out there, but the main thing is that ethonol attracts water which leads to corrosion, and the turns the tiny passageways in the rubber carb kit to mush.
The b&s carb kits are very cheap, under $15, and any small engines place will have them in stock.
They're easy to f up, so take care during install to not tear the diaphragm on the spring, or misplace any of the clips.
http://www.youtube.com/watch?v=DqPXjtWO0KE
Part 1 of 3, the rest are on his "channel"
It looks like a very good video, and he explains everything very well.
~Nate