It is indeed. Out of print and only a very limited number ever printed. Fortunately since Seth is apparently disinterested in getting it reprinted to sell there are many electronic copies available online: http://freshwaterinvestor.files.wordpress.com/2010/04/margin-of-safety-seth-klarman-ebook.doc
So far it reminds me very much of "The intelligent investor", just with a different angle on things and even less academically targeted.