The last GG's CM that I can find is from 2003. Oddly enough it looks very similar to Mr Howard's 2006 one (but I suppose when you've read one, give or take a reference or two to recent major events, you've read them all).
Has Mr Howard instructed (or "advised") the Governor General not to issue Christmas messages? I would be surprised if he hadn't.
Devaluing the office of G-G is one means of preparing Australia for transition to a republic but doing it by stealth will mean that when the opportunity arises to change our constitution to a republican one it will be harder to argue the case for having a President with some real powers. I'm not saying that this will be necessary or desirable but without seeing further and better particulars I'd like to keep as many options as possible on the table, not under the carpet.
In the UK this year, an alternative Christmas message far more radical (I think) than anything the GG is likely to put out here has been given a platform, as The Age reports.