I was working security at the Embassy when most of the FTA people were sorting it out with the Americans.
Of what I recall, tarriffs and import taxes will be phased out over the next ten years. This is to protect Australian economies and votes, as opposed to imeediately. wheather or not this is a good thing is all a point of view I guess.
The FTA will be enacted either jan 1 next year or the start of this financial year. I can't quite remember.
But don't expect an impact on things you can buy for a while yet :(
I'd expect in about 10 years though the car market will remain largely the same... As we saw with the GST, tax lowering only raised the profit margin for business in many cases, not lowered the cost.