i can completely sympathise.  I sent a parcel to Sweden in early November (it was an expensive item too).  It was tracked as far as leaving Brisbane international airport and then nothing until about 2 days ago (now it's still sitting awaiting customs clearance in Sweden).  I have been fortunate that the buyer has not lodged a case with eBay.  

Australia Post are practically useless, the timeframes they talk about to resolve the cases are far too long if you happen to be selling with eBay.  And the estimated timeframes that eBay provide are much too short. However, I would lodge a claim with Australia Post- , if the parcel doesn't goes missing - you should be able to get $100 insurance claim which I think is included.