I bought my copy of the screenplay in the Historic Scotland shop at Doune Castle, where Terry Jones gives a good audio commentary for visitors that includes details of some of the film's shooting. The book is a little disappointing in not containing any `extras', but it does include some stills from the film (in black and white) as well as the amusing opening credits, and a full cast list.
The screenplay also includes directions that are amusing but of which the viewer would, of course, be unaware. An example is where the female doctors in Castle Anthrax attend to Michael Palin. The doctors here are instructed to touch him "in a just possibly medical way." And this original screenplay also shows where changes occurred between script and the final shoot, such as the form of the amendment to the `Knights Who Used to Say Ni'.
I am of a certain age which makes me one of those `sad' people who can quote to you extensive extracts from the script of `Monty Python & the Holy Grail'. But it has not been a complete waste of money for me to purchase this book. Not only does it contain references to physical details in the film that I had not spotted before, but when my partner states to me that `One day, lad, all this will be yours', I can not only wade in the pond of delight at being still called a lad, I can confirm that my response concerning the curtains will be word-perfect.