I became interested in the Moleskines from reading (all of) Bruce Chatwin's books.  I use the small Cahiers (pocket notes, ever-ready for jotting and aide de memoire for everything); the large, plain notebooks - the perfect journal, cannot be beaten; and the extra-large, square-ruled Cahiers for working on guitar designs, design ideas, construction ideas, floor plans, mechanism sketches, etc., etc.:  they are my design journals.