From what I gather, their main revenue is ad money. The fee to join is mostly a gatekeeping thing. It is not a big part of the revenue model. Matt managed growth really well (from what I gather) by limiting new memberships and what not. It is a community and limiting new memberships and putting in a gatekeeper fee seems to have done a lot to avoid eternal September and what not. That's the main thing you need to do to make money from a community: Keep your eye on the prize of making it a good community. I have seen that failed elsewhere.

I don't know much about google algorithms but if you don't have the good community piece of it, you have no business model for this. It is not HN, HN is the funnel for applicants for Y Combinator, so it is part of the business model here but it is a very, very different model. Mefi exists solely (as I understand) to be a community and not to serve some other business need the way HN does.

I think they should make the donate button much, much more visible but I am not a fan of recurring membership fees. But I don't have time to write more at the moment.