Andrew Martin and Kevin Quinn have put together an awesome visualization of the shifting ideologies of Supreme Court justices. I'll buy the directional shifts of individual justices, but Gelman is right that the overall chamber scores just don't make much sense. No way is the current court more liberal than the one that ruled on Roe v. Wade.
Correction: The data above come from Andrew Martin and Kevin Quinn. The visualization was assembled by Carl Roose and Alex Lundry. Apologies for the error.