Charles Talleyrand wrote:
Hovercraft and surface-effect craft are not regulated by the FAA.
How
high must one fly before one falls under the pervue of the FAA? Is
there an official definition of "aircraft" that excludes hovercraft
and
surface effect vehilcles?

The federal gov't (currently the FAA) controls the "navigatable
airspace", per a ruling by the Supreme Court in the early part of
1910's. If you alter air traffic, you'll get a visit.

-Robert, CFI