As a WOO, I would say it is the fun I find in engaging people on their level. Making connections with others feels good.
Discipline to me is the need for precision and predictability, finding pleasure or comfort in routine.
Developer is the joy found in seeing others improve, even incrementally. I work in a high school with several strong high need special ed. programs. All of the wonderful teachers their are developers with these profoundly needy students.
Note: I am new to the field specifically, but have been a counselor for well over twenty years.
As someone with a strong Discipline theme, I find that I like to work on projects or tasks that don't require a lot of vision, but that have more practical or tangible applications. This isn't to say that I don't like vision activities (ex: Strategic Planning), just make sure that we're staying on task and on target with these types of projects.
Systems and order excite me, and I tend to thrive and succeed in projects that tie in with those things. This theme also seems to play out for folks that have an ability (and often a desire) to work on projects on their own (which I see play out with me).
At times, I also find that my colleagues route perceived "problem people" to me to "set them straight" on issues. While I don't thrive with conflict, I don't have issues working through problems and hurdles with individuals. I don't believe conflict intimidates folks with strong Discipline themes (purely my opinion).
I recognize that it's not a definition per se, but it is how I find that the Discipline theme plays out for me!
Woo is about networking and making connections quickly with people. Woo people tend to like to be liked. Woo makes me think to what I heard about Bill Clinton - he could easily work a room, but he would seek out the one person who disliked him most in the room and try to make that person like him or "win" that person over.
Discipline is about liking structure and routine and the ability to create it when it's not there.
Developers are people who not only get a charge out of small, baby-step growth out of people, like Kevin said, but also good at bringing that out in people. The main judicial officer for our campus has Developer and she's excellent at helping students see the poor choices they made and getting them back on the right track.
Woo - draw energy from interactions with others.
Discipline - see the benefit or value in routine and regimented activities. Can easily create processes to accomplish tasks.
Developer - sees the potential in others and work to bring that out of them.