Barack Obama picked Sonia Sotomayor because she's Hispanic, female, and is willing to put liberal political concerns above the Constitution. That checks a couple of important political boxes for him and gets him a liberal judge on the court.

Happily (well, as happily as it gets under these circumstances), Sotomayor will be replacing David Souter, who's also a liberal, so she shouldn't cause any sort of major shift on the court although she could move things to the left on a handful of issues where Souter behaved contrary to form.

If the GOP had another 10-15 senators, after the way Democrats treated Alito, you might see them force Obama to take a moderate nominee -- "might" being the operative word there given the wimpiness of the Republican Party -- however, with 40 Republican senators, the chances of a GOP filibuster are practically nil.

Once you get past those two central issues (What sort of judge will she be? Will she be confirmed?), everything else about this selection will likely turn out to be "sound and fury, signifying nothing."