Electrostatic speakers do sound great, but that's a different technology, not really doable in an iMac enclosure. I'm talking about something like either NXT flat panel technology or a set of resonance drivers.
Resonance drivers attach to any flat surface to in effect turn that into a speaker. Sound quality is questionable, but only because there's no way of knowing what sort of surface some of the novelty items out there would be attached to -- what material, what dimension, what size... In a fixed application you could definitely tune the driver to produce a natural sound curve, which is what NXT does with their speakers, though I'm not quite sure if NXT's can be called a resonance driver???
Would vibration interfere with the display? It's shouldn't: NXT's drivers only excite a vibration of 40 microns across the surface of the "speaker" -- you shouldn't notice it if implemented right. 4/100ths of a mm.
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