I think carb cleaner is the best at removing carbon. Seems I remember trying brake parts cleaner when I last tore down the engine in my car, and it barely made a dent in the carbon, but the carb cleaner just melted it right off.
To the folks worrying about E10 fuel, I'd venture that the problem is NOT the ethanol content. Methanol and ethanol are two of the most simple alcohols, and they burn clean. The problem is that ethanol is 105 octane (basically race fuel), and so to get your 87/89/91 octane fuel mixtures, they combine the ethanol with absolute crap base fuel (like 80 octane or something). Don't quote me on this, just a rumor I've read, therefore it must be true.
I'd again note that there are TWO carbon-based fluids in the engine that can cause carbon fouling: fuel and oil. Both are possible, but I'd venture that you'd have to be running pig rich to get a ton of carbon fouling from the fuel. Also, I'd note that engines can still run pig rich even with computer-controlled fueling -- such as with a "false lean" condition. Oxygen sensors only detect oxygen, so if excess oxygen finds its way into the exhaust (from exhaust leaks, misfires, hanging valves, etc.), then the computer will compensate by needlessly adding MORE fuel. (Another part of me wonders if we're running the correct heat range plug to keep things clean for this engine, but that's another discussion).
Apropos of nothing:
After hearing these stories, I had already intended to tear into my bike to seal up the ignition coils today, but while I'm in there, I'm going to try to install a catch can on the crankcase breather to see how much oil/vapor is making its way to the air box. I'll give it a few months and post any incredible results.