I ran a truck on it for a while. I've got a couple points to make on it, and I disagree with some of what's been said so far.
For starters, E85 attacks old rubber. You'd need to replace your lines and seals in the petcock with neoprene or they'll get soft and leak. Fortunately the carbs don't have much rubber in them, but the fuel lines and the O-rings where the lines enter the carbs are a must-do.
Secondly, E85 (and alcohol in general) is a higher octane rating than gasoline. I think it's pushing 106ish (nearly that of CAM2). You can get away with higher compression (much higher, like 12:1 if need be) without detonation. That's why some drag racers run it. It also burns cooler and slower, so you need to advance the timing. If properly tuned you can extract more hp out of an engine running E85 with the higher-compression and the advanced timing. This will roughly make up for the disadvantage of E85 having less energy per unit volume. i.e. preoperly set up the actual fuel mileage change is negligible, but you have to be prepared to fully convert the motor. If you just rejet to run E85 you will lose around 20% of your fuel mileage. If you do the full conversion and raise the compression and alter the timing and all you are then stuck running E85 (but you've got more hp).
E85 doesn't hurt valves or valve seats, so you're fine there, and it isn't a danger to any of the engine gaskets unless you leak a bunch of it into the crankcase or something. It's just the fuel system gaskets and hoses that are in danger.
You don't need 50% more fuel delivery. I opened the jets of the carb up around 12%-15% on my truck before it was where I wanted it, and then retuned the screws as necessary. That's roughly equal to the reduction in energy per volume, so it makes sense you'd need that much mroe fuel. I ran the timing way advanced, like 25*+ at idle, before I got any knocking and this was an old old truck ('66 Chevy). I did lose some mileage, though, because I did not want to go through the additional money/effort to increase the compression ratio.
Another minor disadvantage is that alcohol attracts water. Dry-gas does this to get water out of your gas tank, but in a tank mostly full of alcohol you'll find that it needs to be drained if it's gonna be sitting for a while or else it will gather a lot of moisture.
In the end, the only reason I'd convert another vehicle to E85 is for a high-horsepower application. The advantage of the timing advance and copmpression increase, as well as the fact that it runs much cooler, makes for a great performance motor. I think it isn't worth the expense, either for modifications or fuel costs, to convert just a daily-driver to it. lack of availability means you can get stuck somewhere if you don't plan your trips right, and you will lose some mileage unless you tune it extremely well, including changing sprockets to take advantage of the higher horsepower.
Also, the reason it's E85 and not 100% alcohol is because while alcohol is a higher octane rating, if pretty much refuses to evaporate below like 50 degrees. To start a vehicle on straight alcohol on a cold day requires fuel pre-heating. The gasoline percentage in E85 is meant to make sure the fuel is still capable of igniting at lower temperatures, and once the engine is even slightly warm (a few seconds after starting) the warmth of the engine will keep the alcohol evaporating. This is another disadvantage in something like a CB750, or especially a bike that's kick-start only, because E85 engines are very cold natured even on mild days, and in the winter forget about it.
