Forums are not maintain by myself users keep posting on it and they might copy it from their own blog
You can't control the duplicate content on forums. But since there's lot of people who would reply in a thread the page will look different.
Having ANYTHING that is duplicated is frowned upon by search engine spiders like Google. You'll definitely feel it by checking your rankings. Yugo,
mentioning source isnt a solution, wont help. its hard to control the duplicate content on forums. in many cases people ask the same questions over and over with almost same answer.
It will be strange if no duplicated content on forums. You can go to avs forum and you always meet duplicated questions what and where to buy HDTV...
Ya agree with the people here. You cannot stop users to add duplicate content. If you are serious then better your forum should contains unique content.