Forums don't make much. I get a few occasional clicks but that's about it. If I can break even to pay for my monthly hosting fee (~$10), I feel lucky.
I also think forum can not make a lot money but maybe it better than for sell backlink or banner ? Do you think so ?
The best Adsense optimized forum I have ever seen - Work at home Forum The owner is a very good guy. The forum has good value and culture in it - Hence whooping traffic and whooping Adsense revenue.
Forums can make millions and can make 0 . Depends on many factors - most important how you monetize it. You can make paid membership lets say 27 per month, and you need just 4 people each month to make more than 100$ a month But would you be able to provide enough quality for them to pay you each month ? And You can have 100k visitors every day and not making anything because of the niche and poor ad placement.
Its not hard to make money from a forum, espically ones with large traffic volumes and large audiences.