Linda Greenhouse has an interesting article in the New York Times reporting on and speculating about the cause of the very surprising number of 5-4 cases at the Supreme Court so far this term: So far only 1, and in a statutory case.
Some of Greenhouse’s possible explanations strike me as plausible, although some strike me as quite unlikely (such as her theory that Chief Justice Roberts was chastened by a critical paragraph in Richard Posner’s new book). My own speculation is that part of it is just a coincidence; a lot of cases decided so far this term were just lopsided by nature. Also, I would guess that part of it is the Justices settling in a bit with each other and realizing that they need to pick their battles more carefully than they did last Term.