A tip-based question-answering system sort of like Google Answers would give users a chance to pick up some money by answering math questions. The content of these answers would be available under the FDL and could be used in the encyclopedia. Furthermore, if PM took some percentage of each tip, this could be a way to generate revenue for the site.
We could combine this idea with a membership drive, so that only a member could collect tips by answering questions. --jcorneli