I saw this covered by a consumer affairs
person on TV. He warns that while this
is a great deal there are other rules that
need to be considered and you need to know
exactly what those rules are before you proceed.

#1 is if your clunker doesn't get the correct
MPG compared to the "NEW" vehicle you are
buying that $4500.00 will be reduced

#2 Remember the trick to this is make the deal
for your "NEW" car deal first.
Then when your done they have to credit you the
$4,500. If you mention it before they can try to
pad the price of the vehicle.

No you do not get a check for $4500.00.

There are other rules that need to be considered

Here's the final authority on the rules... the government:

CARS.gov - Car Allowance Rebate System - Helpful Q&As for Consumers - Formerly Referred to as “Cash for Clunkers”

Wonder if those 4500 eco dollars is BMW passing the 4500 trunk money on to the customer in the guise of being "eco-friendly". The 4500 Cash for clunkers on TOP of the 4500 BMW factory to dealer incentive would make it a deal too good to pass up on, unfortunately an X5 does NOT qualify for cash for clunkers as it MSRP's above $45k.