How many people filed a federal income tax form in the united states of america in 2008?

Question

How many people filed a federal income tax form in the united states of america in 2008?

Answer 1

billions, not just 2007 returns but any unfiled tax return from 2002 thru 2006 because if not in full compliance IRS would hold the refund and the stimulus until  all returns were filed.

Answer 2

143,138,000 as of 5/16/08 per the IRS.