Based on this, it seems like it did http://blockchain.info/p2sh but it seems I can't find a definitive answer.
Yes it did, on April 1, 2012.
[removed link to chain of orphaned blocks]
Yes, it did.
BIP: 16 Title: Pay to Script Hash Author: Gavin Andresen <firstname.lastname@example.org> Status: Final Type: Standards Track Created: 2012-01-03
(Final is the stage after being accepted - it means that it's done.)