No danger posed whatsoever assuming you already have the fuel system to support it, but kinda useless without a tune to take advantage of the higher octane rating.
I plan on going the E85 route at some point in time. There are 4 pumps in Lincoln alone that offer it. Matter of fact PDX made it pretty plain the gains from E85 in terms of power would be substantial when compared to regular 91 or 92 premium. It's cheaper than Sunoco 100 so E85 FTW.
That being said, I'd probably have my AP and a regular premium realtime map at the ready at ALL times.