Having looked at this recently from an Irish angle it's a very grey area. It can be argued that a forum is a database and Irish copyright law states that the first rights of authorship in a database lie with the person who is compiling the database or has commissioned the database to be compiled.
There's actually a whole section of the law that specifically deals with this.
http://www.irishstatutebook.ie/2000_28.html
Look for
Part V Databases