it's pretty universally considered that most of the "clunkers" cars sales are just cannibalizing future sales. A sleigh of hand trick to boost Q3 sales, which will lead to a double-dip in Q4-Q1 2010.
just like the rest of the "stimulus" the effect is do you want it to hurt more now or later? clearly this administration goes for "later".. it's like trying to fix a heart attack with a band-aid.

NEW YORK – Hundreds of auto dealers in the New York area have withdrawn from the government's Cash for Clunkers program, citing delays in getting reimbursed by the government, a dealership group said Wednesday.
The Greater New York Automobile Dealers Association, which represents dealerships in the New York metro area,said about half its 425 members have left the program because theycannot afford to offer more rebates. They're also worried about gettingrepaid.