The Rehnquist Court tradition was to give a new Justice a unanimous opinion for his or her first assignment. The media is reporting that that's what happened today with Mohawk Industries v. Carpenter.
I call B.S.
Justice Thomas filed an opinion concurring in the judgment (in part), so the Court was not unanimous except as to the judgment. What's more, Thomas decided to talk a little trash about (of all things) one of the very things for which Sotomayor was criticized in the debate about her confirmation -- making "value judgments" and subordinating a statute to what she "thinks is a good idea."
For a guy who is so good at holding his tongue, he picked a bad moment to speak.
UPDATE: This article confirms the existence of the tradition of assigning a new Justice a unanimous opinion -- though it has been pointed out to me that the Court did not follow the tradition when Justice Breyer was the new Justice. The current Chief Justice is, if anything, a bigger fan of unanimous opinions than was Rehnquist, so the departure from the practice of unanimity seems a bit more noteworthy here than it might otherwise be.