This is essentially another welfare program.  The Gov't isn't crediting anything.  We the tax payers are subsidising it for these benefactors.  It's one thing to help people with food, but purchasing new cars on my money?  Gah!

Even if Obama gave me 10,000 bucks I still wouldn't drive a 4 cylinder lawnmower

And don't forget the pfff lil kick back for the middle man?

destroy working cars. check

create more pollution. check (destroying cars and making new ones causes more pollution than letting low efficiency cars run)

destroy the low income car market, harming the poor. check.

destroy the low income car market, harming small businesses. check.

get people to sign themselves into debt by turning in a fully paid working car, and then buying a much more expensive car on debt which they only partially subsidize. check. (by definition, all replacement cars cost more than the 4500$, or the dealer would have turned it in himself)

Congress: We have concluded that the plan is a GREAT SUCCESS