Some, I noted, had to do with the "happiness" that creativity can bring with it, the pleasure of creation, that feeling you get when at your desk or in your studio and hours fly by without your even noticing. You're "in the flow"; you're "doing what you love." This is one definition that I share.
Some noted the disconnect between fine and commercial creative activity, and the different measure of success between the two. On the commercial front, it's fine to set a standard of financial return, security, even wealth; but those things can be at best distractions, at worst the source of suffering for the "fine" artist.
Some mentioned "recognition," "being known," or "having a willing audience" for the work they do. And of course there are many different levels here--all the way from the circle of admiring friends to the mass market, and national or international celebrity. Not all of us can be John Grishams or Damien Hirsts. And celebrity can be the enemy of creativity, or its nemesis. Think Sarah Palin. Not many writers, like myself, are impressed to find her at the top of the best-seller charts!
Others still have mentioned personal satisfaction and the fulfillment of personal goals, even the resolution of personal problems like "breaking through your fear." What comes through is the wonderful diversity of responses, how we all manage to find different ways to live the creative life without necessarily going crazy in this highly commercialized world.
One more thing: community, I think, is a wonderful thing, too. In all our diversity, we can come together and find that we share a great deal in our thinking and our hearts. Each time another person writes in, the community expands and--even if it's a virtual rather than a face-to-face community--there's deep pleasure and satisfaction in that. This, perhaps, also belong s somewhere in the definition of "success."
More of my own thoughts later. Meantime, I'll be happy if yours keep coming!