I haven't seen only but a couple of multi-boxers on my realm, Staghelm. My cousin and I are both multi-boxers and we had another in our guild for quite sometime, but he randomly /gquit and we haven't been able to talk to him since.

I agree that it will probably remain uncommon to see multi-boxers running around everywhere. Not just because it is both challenging and takes a lot of commitment, most people don't like the hefty price tag it comes with. :P