The Department of Justice has just filed its brief in the Sixth Circuit as the appellee in Thomas More Law Center v. Obama. You can access the brief here. This is the first brief filed by the United States in any Court of Appeals defending the constitutionality of the ACA. (Again, the only issue in this appeal is whether the minimum essential coverage requirement exceeds Congress's enumerated powers. The parties stipulated to the dismissal without prejudice of the plaintiffs' other claims.)
Two very quick items of note that I noticed on a quick skim: (1) it appears that Beth Brinkmann (Wikipedia entry here) is taking the lead in guiding the federal government's position in the Courts of Appeals, and (2) the United States has declined to challenge the District Court's decision that the plaintiffs have standing and that their claim is ripe. Both of these developments obviously will affect the other cases.