My only issue with the ruling lies in the interpretation of the disc's height.
"The disc will be created at the height of the caster's waist, and will remain at that height, following the caster wherever he goes."
I read that as saying that the disc cannot change it's vertical height (relative to the surface over which it floats). It will attempt to follow horizontally but cannot follow vertical changes except where a reasonable slope or set of stairs allows it.
Within that limitation, i'd be willing to try out the disc-as-perpetual-motion-machine idea. Of course, i have a special fondness for floating disk antics; i once created a fat NPC wizard (3rd ed) who rode around on a permanent floating disk using a variation of the mage hand spell for propulsion.
"The disc will be created at the height of the caster's waist, and will remain at that height, following the caster wherever he goes."
I read that as saying that the disc cannot change it's vertical height (relative to the surface over which it floats). It will attempt to follow horizontally but cannot follow vertical changes except where a reasonable slope or set of stairs allows it.
Within that limitation, i'd be willing to try out the disc-as-perpetual-motion-machine idea. Of course, i have a special fondness for floating disk antics; i once created a fat NPC wizard (3rd ed) who rode around on a permanent floating disk using a variation of the mage hand spell for propulsion.