Because you will be living abroad - you might be entitled for a foreign earned income exclusion. But that exclusion is not granted automatically - you need to file your tax return to get it.
For the person to qualify for the foreign earned income exclusion - he/she should: -- Work and reside outside the United States for at least 330 days during the year(Physical Presence test), or -- Meet either the Bona Fide test.If the person qualifies, he/she may exclude up to $92,900 - for 2011 in foreign wages -- plus housing allowances.
Please consider this publication - www.irs.gov/pub/irs-pdf/p54.pdf
If you move - for instance on April 1st 2011 - you might be able to claim the exclusion for 2011 prorated according to days your were in a foreign country during 2011.
Here are forms you likely need: