National Association of Realtors (bold mine):
Estimates that about 1.8 to 2.0 million first-time buyers will take advantage of the $8,000 tax credit this year, with approximately 350,000 additional sales that would not have taken place without the credit.
Something tells me the NAR didn't realize the awfulness of that math. Calculated Risk details how ugly this is:
And look at the cost of the tax credit! If NAR is close to being correct, 2 million buyers will claim the tax credt - times $8,000 - is $16 billion. But this only resulted in "approximately 350,000 additional sales".
So this tax credit cost taxpayers about $45,000 per each additional home sold. Not very effective ... especially considering most of these are lower priced homes.