pchorman,
Well, the POD is supposed to stand in for what everything sounds like at the end -- after the guitar signal through the amp through the effects and out the speaker into the mic... Running it through an amp after all that is akin to taking the mic'ed signal from the real thing, then running it back through another amp and set of effects again and mic'ing it again at the end. It seems to me that that would not sound particularly good.
The POD does sound pretty good through a clean amp with the AIR switch off -- but not as good as a good amp with a good effects chain would. It excels as a direct recording device but is only pretty good as a live effects box -- unless you take it through a really good PA system in lieu of an amp.
-AlChuck