A story in yesterday's Washington Post accurately quoted me stating that the liberal Justices seem more frustrated than angry with their conservative colleagues, both because the liberals are losing a lot more cases this Term than in recent Terms (a consequence of the replacement of O'Connor with Alito) and because in a fair number of cases the conservative majority seems either to dismiss or ignore prima facie persuasive objections from the liberals. One of the main points of the story is that despite the ramped up professional pique, personal relations among the Justices remain harmonious. The story quotes Justice Alito and Georgetown law professor Richard Lazarus for this proposition, and I see no reason to doubt them. As I've noted before, Justice Breyer's standard stump speech explains that the Justices' disagreements are about the law but that they like and respect one another across ideological lines.
To me the interesting question is why the media seem to care so much whether the Justices are being nasty to one another behind closed doors. I suppose there's a gossipy element to it. The Justices lead pretty boring lives, yet they wield enormous power, so if there's some way to spice up the story, reporters want to do that. The interest in whether Justices Souter and Scalia are on good terms is a bit like the interest in whether Brad and Angelina are happy together.
Moreover, inter-personal dynamics could explain results in some cases. Many people have speculated that Justice Scalia was passed over for the Chief Justiceship because he was thought insufficiently attentive to the feelings of his colleagues to be able to build majorities. And it's hard to imagine that Justice McReynolds---easily the worst asshole ever to sit on the Supreme Court---did not affect the outcome of quite a few cases through the sheer force of his despicable personality.
Ultimately, I suspect that the discussions of how famously the Justices get along serve two purposes. First, they shore up the Court's legitimacy, which is why the Justices encourage these discussions. At a time when Capitol Hill softball leagues have had to split into Democratic and Republican divisions because of partisan bickering, it's comforting to know that there are grownups running at least one branch of the federal government. Second, the focus on interpersonal relationships is simply easier for the lay public than trying to understand the actual work of the Court. It takes a fair bit of training and effort to see how a Supreme Court opinion misreads some precedent. If the vote can instead be explained by the fact that Justice X hates Justice Y, that's much easier; hence the interest in looking for such hatred even where it does not exist.