I moved from Sweden to Texas in March 2009 and worked as a research scholar on a J1 visa. For 2009 and 2010 I filed tax as a non-resident alien with the 1040NR-EZ form. Days I was present during 2009 and 2010 are excluded for purposes of the substantial presence test.

As I understand it, I am considered to be non-residents for tax purposes during my first two years of presence in the US. This is calender years, right? So that means that for 2011, I should be considered a resident-alien for tax purpose?
However, to complicate stuff; I moved back to Sweden on the 28th of June, 2011. In total, I was in the US for 176 days in 2011.

Am I considered to be a resident-alien for tax purposes for 2011, or am I still a non-resident alien since I was present in the US for <183 days?

My employer started to withdraw FICA taxes (OASDI and MED) in February 2011. If I am still considered a non-resident alien for tax purposes, should I use 1040NR-EZ? And will I get a refund on the FICA taxes?

You are nonresident for 2011 as you did not complete substantial presence test in 2011. You will file nonresident tax return but you will not get FICA taxes back as during 2011 you were not exempt from these taxes.

MukatA is correct about you being a non-resident alien due to NOT meeting the Substantial Presence Test.

To clarify about the FICA taxes, your exemption is a matter of U.S. tax law which allows TWO calendar year of exemption, which, for you, was 2009 and 2010. You became liable for FICA taxes ob 1 January 2011 irrespective of your J-1 visa status.

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Thank you so much for your help and clarifications!

Just to be sure, I then just need to file the 1040NR-EZ, and no other forms (such as for instance form 8843 that I used 2009 and 2010 to verify that I was considered extempt induvidual)?

Actually, the Form 8843 IS required for this year as well.