I think that forums are the toughest to keep active since one member that others do not like could ruin the whole community. Or one day everyone who usually posts 20+ posts per day suddenly stop and wait for someone else to post something new and it never happens.
Forums are GREAT money makers but you need to know how to manage them very well. Provide VALUE!!! Main Forum Income Streams: 1. PPC 2. Your own Products. 3.TEXT link sales. Good Luck, kolaios
On forums I think you first make them active, to have 5-10 users posting daily and then advertise it big. With hard work you can get huge traffic and when you get huge traffic you should find to sell private ads and make contracts with companies.
i didnt run a forum before but i think a established forum is easy mantainance because the content is auto generation and all you need to do is to keep those spammers out