Prolonged lowe power running:
Central electrode glazing occurs when the engine is run at intermediate power too long, and then suddenly high power is asked for during a little period. The condensed particles are glazed onto the electrode before they had a chance to flash off by rising plug temperature.
Hmm... sounds strangely like flying an IMAC/3D airplane... oh well.
Thanks for all the usefull info... much more info than I had on the subject.