Hypothetically speaking, if Judge Sonia Sotomayor were to get nominated to the Supreme Court, there would be six Catholics on the bench, relative to 24% of the overall population. Historically, however, there has been a lack of Catholic representation on the bench, 11 total nominated of which 5 are currently sitting. Needless to say, in recent decades, nominations to the Supreme Court have skewed Catholic.
Of the three other Justices, 2 are Jews, and the remaining, Protestant (Stevens).
(h/t Josh Marshall)