Oh, Project Gutenberg and Distributed Proofreaders are definite good causes, and the sort of thing one can do in one's spare time as one feels like it - like Wikipedia. Not sure they have fantastic leverage, though making good stuff available and (the leverage) making it seem more normal for reading materials to be free content are both good things. PGDP is probably a more productive brain relaxation than Sudoku. (Though I still pick up the Sudoku and haven't proofread anything in years.)