Hawk:
[myth] If an aircraft is not moving (stopped on a taxiway for example), then its not producing any power.
Yeah that one bugs me too.
Eck:
One definition of Power is that it is the 'rate of doing work'.
Work = Force x Distance
If the aircraft's engines do not apply their force (thrust) through a distance, then no work is being done. Ergo, no power is being produced.
Sorry Eck but the engines still do work because even though the aircraft is stationary the engine still blew a mass of air over a distance. Hence willl05's comment about standing behind a running engine to test the theory. Ultimately the 'work' is being 'wasted' in a futile attempt to turn terra firma and the atmosphere in opposite directions but work is still done and power is still produced.
It really just comes down to Newton's 3rd law about action and reaction.