This is a crazy subjective question, especially as people on this site fill all sorts of different roles. As jax says, he doesn't want to be a director but that doesn't preclude him from success, and the guy's a whizz in the camera department and is bound to do well. Alcove and APE do sound work, so, again, that's a different form of success. I make a little bit of money doing freelance journalism, yet another form of 'success'.
Personally, I'm not at the point where I'm looking to be working professionally in film. When I first came to Indietalk I hadn't made anything. Then I made a few shorts and got distracted by going to university (a very good university, does that make me a success?

) and it was another year before I started work on
The Flight of the Flamingo. Now we're almost finished with that, so I'll let you all decide then whether that makes me a success...