Forum Moderators: open
Business: Rely on Relevant Advertising Mainly.. Get a few links at demographic and business relevant content websites and care about how much it's seen and clicked on, nothing else. It's about branding and showing you exist to the most relevant users. Not about getting a better epeen.
95% SEO
Information: If you know any academics or just some of those crazy people who likes to learn stuff and write about it, you have an advantage. If not, you'll have to go chase links all over the internet which are relevant to the topics you're specializing in, while you're genius is just lying on the internet without getting any attention.
15% SEO
Services: Depends alot on competition. If you can deliver a service, you can bet that somebody is also going to deliver it when they catch on to a profitmargin. Not always a good thing to go global, local can be much more beneficial at times, but depends on what you're betting on really and how wide and broad the "needers" are.
50-75% SEO
Entertainment: Social Networks especially ... everything you can get in touch with actually without being a spammer and which can get you some of that laughing, screaming and hysterical traffic. You won't get that much traffic from search engines unless you're really popular anyways on one-two keyword types, since the search engines are much more information based, and the algorithms just haven't developed a sense of humor, yet. GOOG is working on it I think.
50% SEO
Hobby: Write it to your friends on a IM. Then join a forum or three about your hobby. Have the link in your signature. Have fun.
5% SEO