It may end up being great for the environment. It will certainly make some car dealers very happy. But that Cash for Clunkers bill just signed by President Obama may not be the sweet deal that consumers were awaiting.

True, the new program offers to pay $3,500 or $4,500 for old, gas-guzzling cars and trucks that are traded in for new, more efficient vehicles. Add that cash to the new-car sales-tax deduction that was in February's stimulus bill, and it looks like the government is making a car deal you can't refuse. But while the government's plan may benefit some buyers, it's not for everyone. "A lot of people will be disappointed," says Philip Reid of Edmunds.com, a car research Web site. "This is not like winning the lottery."

One reason: embedded in the program's fine print are several rules that will disqualify a large segment of drivers when the two-month plan is expected to kick off near the end of July. Cash for Clunkers works like this: cars getting less than 18 miles per gallon (combined city/highway), owned, registered and insured for at least a year, and from 1984 model years and later can be traded in for new cars. The dealer pays the owner $3,500 (if the new car gets between 4 and 10 more miles per gallon) or $4,500 (if the new car gets 10 or more miles per gallon.) The dealer then is required to scrap the car so that it doesn't end up back on the streets. The dealer is then reembursed by the federal government.