Sujit Choudhry & Richard Stacey at The Center for Constitutional Transitions at NYU Law and in conjunction with International IDEA have just published a really nice study of semi-presidentialism and Tunisia. It is available here.
The interest lies less in the Tunisian element. The paper is a study of the April draft of the proposed Tunisian constitution. As I understand it, there is now a new draft and there may well be another version soon. So, some elements of the study may have a short shelf life.
Instead, what is nice is the comparative aspect and, in particular, the details about presidential and other powers in semi-presidential countries more generally. In particular, there is a great comparative table at the end. The study looks 38 countries that are all unequivocally semi-presidential as defined by this blog. So, the paper generally and the comparisons in particular will be of great interest.