Yeah, I started to mention yesterday that there's always a gap between the legal definition and the enforcement. That said, however, problems tend to ensue when one has "a problem," especially one in which liability might become an issue. Therefore, I tend to recommend compliance to the letter of the law, even when it is unevenly enforced.
The current "legal definitions," as far as I can find, are (and pardon the length and verbosity of this):
"Moped" means a device upon which a person may ride which has two or three wheels in contact with the ground, a motor having a maximum power output capability measured at the motor output shaft, in accordance with the Society of Automotive Engineers standards, of two horsepower (one thousand four hundred ninety-two watts) or less and, if it is a combustion engine, a maximum piston or rotor displacement of 3.05 cubic inches (fifty cubic centimeters) and which will propel the moped, unassisted, on a level surface at a maximum speed no greater than thirty miles per hour; and a direct or automatic power drive system which requires no clutch or gear shift operation by the moped driver after the drive system is engaged with the power unit.
"Motorcycle" means every motor vehicle having a seat or saddle for use of the rider and designed to travel on not more than three wheels in contact with the ground, but excludes a farm tractor and a moped.
"Motor scooter" means every motorcycle with a motor which produces not more than five horsepower, but excludes a moped.
"Motor vehicle" means every vehicle which is self-propelled and every vehicle which is propelled by electric power but which is not operated upon rails, but excludes a moped.
This excerpt was copied directly from this site:
http://www.capitol.hawaii.gov/hrscur..._0286-0002.htm , which is a subpage of the state government's 2007 (apparently) legislative site. What caught my eye, as a former motorcyclist, were the specific power, engine size, and speed constraints, which seemed somewhat confusing and overlapping. Again, my hesitancy in saying "go for it!" is not in what one might do, but in what might happen were one involved in an accident.
The driver test is not hard here. Many people don't even study the book before they take it. I do not recommend this, but it happens. If there is no compelling reason not to take it to be fully "legal," I'd take it for liability reasons.