I haven't run that many dragons in my DMing career. One or two, here or there, usually as NPCs, not actually intended for fighting. Which is no way to run dragons. The occasional wise sage/enemy to be bargained with is fun, for a change of pace, but dragons are for slaying. That's actually one of the few things that bugs me about Eberron, that the "great dirty lizard on a pile of gold" trope isn't really workable.
Part of it is that I really haven't run that much D&D. I've run plenty of d20, but my two long-running games used d20 Modern (which I want to get back to, someday) and Arcana Evolved. I've only ever ran one even mildly successful 3rd Edition D&D game.
But still, no excuse. So this current game I'm running, once they finish up Keep on the Shadowfell (or if they decide it's not worth their time; it would still be interesting if the cult succeeded at what they're trying to do) there will be dragons. Possibly several dragons.
Great horrible dragons, sleeping on piles of gold.