This has been a question faced by many people. Mostly by those who do creative-oriented professional work. To help guide someone who still weighing in their options, here's a graph that might help you make a decision.
Come to think of it, there was no pro-bono work I've done for people that never really satisfied me. And with my track record, I've felt the person or the organization got more out of the arrangement than me, so I stopped doing pro-bono work. But maybe because Im bad at negotiating.
Have you ever regretted working pro bono for a person or an organization?
The whole image can be viewed
here.