Precisely because I am a fan of both, I have made a conscious effort to keep them minimal. Moreso dragons than dungeons, since I am a mega mega fan of dragons and just generally kind of like dungeons.
That doesn't mean I don't use them. I do. But I have put in the effort to make any dragon that shows up special. The party has encountered a grand total of five dragons over roughly seven years of play. One of them is, in fact, a newly-joined player! He's just a dragon that got stripped of his powers by the Celestial Bureaucracy. They want him to reform, not kill him, so they are hoping that partially-supervised rehabilitation in the mortal world will serve to curb his more problematic impulses and allow him to return to working for the greater good.
I don't often use "dungeons" in the strict sense of a place beneath a castle (or other similar building) used specifically for keeping people prisoner. But the first location the party went to investigate was, in fact, a dungeon...and also a pretty nasty laboratory for mortal-kind experimentation, a very long time ago.