Writing at Slate, University of Chicago law professor Eric Posner claims that Supreme Court Justice Anthony Kennedy "is a libertarian" because "he's (somewhat) liberal on social issues and occasionally skeptical of the executive, and conservative on everything else." Moreover, Posner argues, "Because Kennedy is so often the swing vote, it is more accurate to call this court 'libertarian' than 'right-wing.'"
Any discussion of Kennedy's purported libertarianism has to start with his positions in the medical marijuana case Gonzales v. Raich (2005), where he voted in favor of an expansive reading of federal power under the Commerce Clause, and the eminent domain case Kelo v. City of New London, where he voted against the property owner. These decisions are about as un-libertarian as it gets.
Still, Posner does raise an important point. As I wrote in a column last year, Kennedy is "the one justice currently on the bench who at least occasionally favors the basic libertarian mix of social and economic freedom." He's the only justice who has voted in favor of gays and guns while also opposing Obamacare.
Does that make him a libertarian? Not quite, given his larger record. But I do think it's fair to say Kennedy's views have helped push the Court in more of a libertarian direction.
At present, that's probably the best libertarians can expect from the high court.