Shakra is correct in that we do not have a freedom of speech ruling as part of our constitution. What we do have is the rather large grey area of slander and defamation.
I personally feel that for a public forum to be brought into court would be a hard battle as the forum is open whoever is being spoken about has the means to reply on the same level as anyone else.
But like most things in the legal field, if you can afford a good lawyer you can get away with more - just ask John Laws!