Jason Harrow (SCOTUSblog) tells us how unusual Justice Kennedy's 97% batting average is. (Kennedy was in the minority in only 2 of the 71 cases he participated in this Term.)

Even Justice O'Connor, whom some used to refer to as the "most powerful woman in the world" due to her position in the center of the Court for many years, never had a Term like this. Her most successful Term was OT03, when she was in the minority five times and wrote two dissents; still, in that Term, 4 of her 5 dissenting votes were cast in 5-4 cases (there were 19 5-4's in OT03).....

One must look way back in the Court's history to find any single Term where one Justice had comparable success. Justice Kennedy's two dissenting votes tied Justice Brennan's output in October Term 1968; with a larger caseload back then, though, Justice Brennan's feat that Term is arguably more impressive. Still, one must go further back to Justice Byron White's October Term 1964 to find a circumstance where a Justice bested Kennedy and dissented only once over the course of a full Term, with no extenuating circumstances such as justice turnover (which can lead to misleading numbers).

The bottom line is that, by most measures, Justice Kennedy's October Term 2006 has been the most successful Term by a single justice in roughly 40 years.