Judge Sotomayor's most controversial case right now is the New Haven firefighter's case, where she upheld the city throwing out the results of a promotion test because they would have led to a promotional scheme inconsistent with the mandates of Title VII. The firefighters (mostly White) who lost out sued, alleging discrimination.
Reasonable people can disagree on this case (Ta-Nehisi Coates, I know, has been skeptical). But it is important, for those who wave "activist" like a talisman, to remember that this is a case of the judiciary deferring to democratically elected officials on matters of social policy. The closest thing "activism" has to a principled definition is "striking down democratically enacted laws" (and, ironically enough, it was the conservative wing of the Rehnquist court that made it the most activist Supreme Court in history). But the popular definition of "activist" is "judge who makes a ruling I dislike" (see also, Kelo), so I doubt this observation is going to deter much of anyone.