I just read this book again. I love it. I recently purchased my own copy, along with a copy of the sequel, The False House. It had been only a couple of months since I read The High House, but since I was about to read the continuation of the story and because I loved the book so much, I decided to read it again so it was fresh in my mind. I enjoyed it just as much the second time through, and was more attuned to some of the allegorical elements.
This time I read the entire book in one day - that day being the travel day as we came home from our Honduras mission trip. This small book fit easily into my purse and I was able to read it as we traveled from San Pedro Sula to Miami, during our long (otherwise boring) layover in Miami, and then from Miami to Baltimore. And I still had time to visit, nap, browse a magazine or two, and do a couple of Sudoku puzzles. That's more a commentary on how LONG the travel day was, not on how fast I read. 
My first "review" of this book can be read here.