Depends on the setting. Planescape can absorb them pretty easily, but I'm not sure I would use them in Eberron. My current homebrew would actually absorb them pretty well:
The dwarves, exiled from their traditional home, have been taking over the homeland of the lizardmen over the last several centuries. The whole interaction has a lot in common with the European Settler/Native American conflicts in America. Since the dwarves hate dragons (it was dragon who drove them from their home in the first place), I think they might apply the term Dragonborn to the lizardmen as a pejorative.