I usually do ''bottom'' end in Mono, main synth part in mono, then back ground synth and hi end percussion in Stereo. I play my music through our rig (Punisher's, X-Tro's and Void amps, for any speaker geeks!) in Mono, and I don't notice any muddiness or loss of definition. I would imagine if you used ''extreme'' panning in your tracks then play back in Mono might alter the sound a little.

Like Jay Pace said; as long as there is bass, most of the punters/munter's couldn't care less.