What policies should be adopted regarding content on discussion forums? Should the people who post own the content they have posted, or should the site hosting the content own it—or should it be there...

What policies should be adopted regarding content on discussion forums? Should the people who post own the content they have posted, or should the site hosting the content own it—or should it be there for the taking by anyone? Explain your reasoning and identify who should be responsible for content that is libelous or potentially harmful.