The Office of the Solicitor General has filed the United States's brief for the petitioner in HHS v. Florida (No. 11-398), addressing whether the minimum coverage provision exceeds Congress's enumerated powers. You can access the brief here.
UPDATE: Nothing terribly surprising after an initial skim. I would note the following items, though, as somewhat interesting: (1) the United States puts the integral-to-a-broader-regulatory-scheme argument first in its brief; (2) nonetheless, it devotes considerably more space to the "pure" Commerce Clause defense, that the minimum coverage provision is itself a regulation of economic activity (pp. 33-52); (3) while the overall content of the brief looks very similar to what we have been seeing from the government for the last year or so, this brief seems to do a more careful job of framing this case as being solely about legislative means, rather than ends; and (4) the SG has decidely not abandoned the taxing power argument, devoting a full 11 pages to it.