Yesterday I cleared the Extending exam.
It had 48 questions with 700 as passing score.
I had referred the official training material of CRM 2011 as the training material for CRM 2013 are not released yet. Apart from that I had gone through different articles and videos to prepare for it.
There were very few questions that were specific to CRM 2013. Mostly they were around new methods added in Client SDK.
For someone who has a good hands-on experience in development in CRM 2011, passing this exam would not be that difficult.