In case anyone is reading this thread and becoming pessimistic about their chances of achieving passive income, I'd like to note that there is a clear sampling bias: folks that have found profitable niches are less likely to share their projects for fear of attracting competition. I suspect that choosing a good niche is pretty important when it comes to passive-income type projects. It looks like the most profitable project so far in the thread is il's, and he sold his site on flippa, so competition is now someone else's problem.
Just to test this out, if anyone is staying quiet about their project for fear of attracting competition, could they please reply to this comment and say so? Don't worry, your silence is totally understandable :)
(The sampling bias will probably still remain somewhat due to folks have their projects linked to from their profiles and not wanting to remove them.)