Over at the Volokh Conspiracy, David Bernstein slightly underestimates the diversity of the Federalist Society's membership:
The media's new obsession over whether John Roberts is or was a member of the Federalist Society is pretty foolish. I know members whose political views range from moderate conservatives (more moderate than, say, O'Connor or Kennedy) to Christian rightists to libertarian anarchist individualists. Judicial philosophy ranges from Borkean anti-judicial review views to Randy Barnettian presumptions of liberty. In short, membership in the Federalist Society tells you nothing about a nominee except that he or she is not "on the left", which one presumes would be true about any Bush Supreme Court nominee.
(emphasis mine) Actually, I know at least one left-wing, Kerry-campaigning, certifiably-lefty member of the Federalist Society. Admittedly, I only know one, but then, I don't know that many Federalists.