Update July 2012
McDonald's deals are no longer banned.
Any posting to McDonald's and offer links to McDonalds.com.au are now banned on OzBargain.
I received an email from McDonald's Australia's Vice President this morning that OzBargain "is currently displaying McDonald's register trademarks without permission". All previous McDonald's offers are requested to be removed from OzBargain. While OzBargain is a user-generated content website, all uploads by members still comprise a breach. Therefore I do not wish to risk any future issues, I am now banning McDonald's from OzBargain completely.
McDonald's did mention that "in the future they may wish to utilise OzBargain themselves for the benefit of its members" so I guess they may officially post offers here (but unfortunately no one else can).