Linda Greenhouse's exploration of the relative paucity of 5-4 decisions thus far this term generally overlooks the most likely and plausible explanations: Last year's high proportion of 5-4 splits along ideological lines was itself and outlier and an artifact of the OT2006 docket. Last term had a relatively large proportion of exceedingly close and difficult cases, many of which concerned contentious, high-profiled issues. This term certainly has high profile cases as well, some of which have already been decided, but they have not been decided along traditional "conservative" and "liberal" lines. As a consequence, OT2007 is looking more like Chief Justice Roberts' first term on the Court, OT 2005, than it is OT2006.
Greenhouse's suggestion that conservatives on the Court have been chastened, and this explains the apparent lack of ideological division, is particularly unconvincing to me for two reasons. First, the big decisions in high profile cases (voting rights, child porn, lethal injection, Medellin), have largely gone in a "conservative" direction, just with larger majorities. So if any of the justices have changed their approach — and I am skeptical that any have — it would be those liberal justices who are joining conservative majorities. Indeed, one plausible theory (albeit not one I am endorsing) is that Justice Stevens has moderated his position in several cases so as to stay with Justice Kennedy, in the hope that he can have more influence on the swing justice in other cases.
Another problem with Greenhouse's suggestion that the conservatives have tempered their approach is that the conservative 5-4 decisions last term were not particularly aggressive or ground-breaking (a point I've made before). Few of the 5-4 decisions in OT 2006 made significant changes in the law (and the 5-4 decision that broke the most new ground, Massachsuetts v. EPA, went in a decidedly "unconservative" direction). Moreover, as Greenhouse herself noted at the time, several of the Court's conservatives expressed disappointment that the Court did not go farther.
OT2007 is not shaping up to be any more or less "conservative" than OT2006 (at least not yet). It just features a different line-up of cases, which are more conducive to larger majorities and less spirited dissents. This could certainly change — we have lots of cases to go, and plenty of opportunities for fiery divisions. Nonetheless, if I were to make a prediction it would be this: History will reveal that OT2006 was the outlier on the early Roberts Court, not OT2007.
UPDATE: Ed Whelan adds some thoughts here.