http://www.stefanotatai.com/The IM Stefano Tatai wrote an e-book about the 6. Bg5 line against the Najdorf.
From his site: It is with pleasure to announce that I am finally at the end of my work on one of the most important and fascinating variation of the Sicilian Defense. I refer to the Main Line of the Najdorf: 1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6 6.Bg5 e6 7.f4 Be7 8.Qf3 Qc7. These are the fundamentally characterizing moves, therefore important and also extremely interesting variations will be trated in my next work, that I count to complete within this year.
But let's consider the present The Najdorf Main Line First of all it is an e-book. E-books are, in my opinion, the future. Of course we all, lovers of the traditional paper books, their touch and smell, the look they offer orderly lined up on the shelves of our libraries. What is nicer than sit in a comfortable easy chair, or in front of a desk, and immerse ourselves in the adventure of culture and science? For e-books you need a computer, and the reading on the screen needs a totally different approach, different visualization and, perhaps, differently trained eyes as well. In a way one could think that some pleasure of reading on the paper is lost on the computer. But there are many favorable characteristics, too. To begin with, a paper book occupies space, whereas you can have hundreds - if not thousands - of books on a minuscule pendrive or dvd.
Sometimes it is not simple to find the chapter or wording that requires the knowledge of knowing where to search; in an e-book this is much easier and, coming to chess, the finding and following of variations is as fast as a lightening.
Finally there is another unattainable advantage in comparison with the publishing of paper books, something that appears particularly attractive in the eyes of the authors: when the book is already written, there are months and months of waiting, untill the book is finally printed and made available.
OK, I think I made it clear, that partially the motivation that has driven me towards this solution is selfish. But I insist, that looking at my work, you too will find it appreciable and in a certain way more practical, than a paper book.