Kharon,
I'm not a legal eagle either and I also had my curiousity peeked by some of the posts in another thread, and so I posted a link to a legal website on Defamation/ Libel Laws in Australian Electronic media.
You might find the information is useful.
Australian Defamation Laws and the Internet
The fact that the truth isn't always a defence was an eye opener to me.
How this relates to a professional opinion or professional priveledge, I have no idea.
Seaeagle109
"A Man's character is his fate", Heroclitus, 535-475 BC