It really depends on how the car is tuned. If you get your car tuned with 98 octane, then thats whats gonna get you the best results. Some people have great results with E10 and others cant stand it, and you can put it down to engine characteristics and tunes...
Same goes with the e85 however you're fortunate enough to get a *bunch* of extra power... I read an article Martin Donnon wrote about his experiment with E85, he claimed a 40kw gain on some cars, which makes me sit up and take notice.
The downside being, if you tune your car for E85, then you might be stuffed if you cant find any and have to settle for premium (settle for premium. hah.) From what I understand the ethanol burns cleaner so for those of us who just drive around the place, it means less exhaust dust to clean off our rear bumpers ;P Possibly it could be beneficial for those who have been stung by emissions laws...
You'll only get 80-90% of the range compared to petrol due to the density of the liquid (I think) but if they make it readily available I don't see what the problem is. I'd happy get my GTR tuned for it, provided it didnt kill the seals, pumps, etc... much more preferable to LPG.. plus there is that $ incentive, 50c a liter is a big saving imho
-D