I remember one of the older commentators during an ashes series a few years ago stating that number 3 should be your best batsman, the guy who you can rely on more often than not. Ponting has, for the last few years been a rock in the order and someone who you felt confident would score runs when he walked to the crease. Bowlers were worried, setting defensive fields to him and not bowling anything short because they just knew he was the best puller and hooker in the world at the time. There is no doubt in my mind that he has deteriorated, his reactions look slow, his timing looks off and his ability to steady those around him, a quality he possessed previously seems to have just disappeared.
This is not to say he should be dropped, I completely agree that he needs a new spot in the order and we can just look at the success of two of history's greatest ever batsmen. West Indian great Brian Lara demoted himself to number 5 towards the end of his career and his form took off. Sachin Tendulkar was in the same boat 2 or 3 years ago when he looked to be nearing the end of his career, a move down the order to number 4 resulted in him achieving many milestones that he probably never would have reached if persevered with at 3.
Hussey has to be our 3, Clarke our 4, Ponting our 5, Watson our 6. The rest of the order should be picked on form, potential and contribution to the team.