Not to change the subject--you all keep schwahing and octopodeaning all you want--but I began to think about sjmaxq's observations on the aesthetic appeal of millennia, and I began to wonder about pandemonium:

So I looked it up on onelook.com. It appears to be a regular old noun. One pandemonium--and I suppose one could be pressed to visit several pandemoniums. There wasn't a single listing of 'pandemonia.' Why not? (I know this is going to be one of those Greek explanations, but please do go ahead.)