What I've found is those that have done it successfully are for it and those who haven't done it or failed because they didn't know what they were doing are against it.
It's definitely not for everyone, but it is great if you have a setup that can use it and it is readily available.
I daily drive with it and have two gas stations on the way to work that have it, so that is easy. I have a totally upgraded fuel system to handle up to 600whp of E85 and the car is tuned for it, so that is not a problem either (I"m only using around 500whp of it). The only issue left is longevity of fuel system parts and only time will tell about that. I've got 4 1/2 years of DD'ing on the stuff with no problems.
What I haven't gotten an answer for is if anyone has tried it on the '13 ST yet. So far, no takers...
2015 F150 4x4 3.5 Ecoboost
2002 Camaro SS, new turbo install in progress...
2005 Neon SRT-4, Big wheel stage 3, E85