Many people will simply use premium fuel in motorcycles as a matter of practise, but in most instances, premium fuel is NOT required and can, in certain cases, actually cause problems down the road. High-octane fuel actually has inferior combustion properties as compared to "regular" fuel. When you think about it, this makes perfect sense: after all, the whole point of high-octane fuel is to prevent detonation (heard as a pinging or knocking sound), which is caused by a low ignition point and high burn rate of the fuel. Thus, if you retard the fuel's ability to burn, you raise its resistance to detonation. Using these premium fuels in an engine that doesn't generate high enough combustion chamber temperatures to approach the "knock point" will result in incomplete combustion and faster build-up of carbon deposits inside the combustion chamber.
The lesson learned is this: use the lowest octane fuel that prevents pinging in your engine. If you find that your engine requires premium to prevent pinging, you should consider running a couple tanks of gas through it that contain a combustion chamber/fuel system cleaner (such as Techron; more on that in a minute). A corrolary to this lesson is that fuel additives that increase the octane number of a fuel are likewise unnecessary and possibly harmful.