In the case of Windsor, a women was legally married in NY when her spouse died. She was denied the benefit of the spousal deduction for federal estate taxes.
The court held that Windsor was denied that equal protection. There are several other cases also such as Gil V Office of Personnel Management that the courts have also found the same thing.
Now the question is will those cases only overturn part of DOMA or all of it? Those cases are on section 3 of DOMA, so the court can rule narrowly and force Federal Recognition of marriages by same sex couples.
The court could keep Same sex couples that are legally married in one state from being recognized in other states since that is not a part of either case currently considered.