Since three-wheeled vehicles come up on AutoblogGreen so often, we thought it would be prudent to inform you that Colorado is considering adding a distinct license requirement for three-wheeled motorcycles. Generally, if you have a motorcycle license, the state you live in allows you to ride a motorcycle with a sidecar or a trike, so no matter where that third wheel is located, you do not need any special skills... legally. Anybody who has ridden a bike with a sidecar knows that it is a totally different experience than a bike with a single-track. Also, trikes with their third contact point up front are generally more stable than one with the third wheel in back.
We'll chime in and say that some extra training should be necessary for a sidecar rig, but it's likely that this is less important for trikes. Unfortunately, distinctions such as this are very difficult to legislate, so we'd imagine that any changes will be rather sweeping generalizations and will take place on a state-by-state basis. We'll keep you updated if necessary.