During John Roberts' confirmation hearings, he convinced most of the Senate and a larger percentage of observers that he was two things: (1) a thoughtful, right-leaning moderate and (2) a genuinely pleasant guy. This largely placated many erstwhile democratic critics who feared that Bush was attempting to appoint another Scalia.
As Chief Justice, Roberts quickly demonstrated that he was much more of a banner-waving conservative than he had let on. He has voted consistently (though not uniformly) with Scalia and Thomas, and his reasoning isn't nearly as nuanced as one would expect from a moderate justice like O'Connor or Kennedy. Additionally, it turns out that he's kind of a jerk as well.
Roberts' dissent in Mass. v. EPA was extremely condescending, and he took a sharper jab at Stevens in this week's Abdul-Kabir v. Quarterman, a death penalty case decided 5-4. The Volokh Conspiracy has analysis here. Each of these opinions are reminiscent of the arrogant sarcasm that has made Scalia such a colorful character on the Court and, fortunately, driven moderate justices away from his maniacal jurisprudence. While sarcasm is fun to read, I don't think it adds much in the way of constructive discourse in the context of the Court.
It's looking more and more like Bush slipped a Scalia past us after all.