To qualify for the extended tax credit deadline, service members must have served on official extended duty outside of the United States for at least 90 days during the period beginning January 1, 2009 and ending April 30, 2010. If so, they have until April 30, 2011 to sign a sales contract and until June 30, 2011, to close on the property. Both the $8,000 first-time and the $6,500 repeat home buyer tax credits are included in the extension.
The rule that requires buyers to repay the credit if they move out of their home within three years has also been waived for qualified service members if they receive government orders to move.
For more info: http://www.irs.gov/newsroom/article/0,,id=215594,00.html