I have read and used three of David Williams' books.
I was familiar with and had used a couple of the exercises in this book already: Bayeux Tapestry (a retrospective over a time period in months or even years) and Postcards from the Future. Some exercises in this book (You Must Be Dreaming, Pick a Straw) appear to me to be a bit whimsical; perhaps in certain settings they can be used more effectively. I've used elements from several of the "visioning" exercises (Vision Types, Shared Vision, Vision Test and Vision Shuffle) to craft my own visioning exercises. In this respect, I found the book to be more of spice rack than a frozen-TV-dinner -- and that's fine by me.
Overall, I recommend this book (and others by the author) highly. They represent distilled, practical knowledge for a minuscule price.