I have a copy of the book & map set and really like it. I ordered it by phone from Princess well in advance of my trip so that I could read it ahead of time. (I'm not going on Princess.)
I think it's worthwhile. It covers quite a variety of information including history, things to do, fishing industry background, detailed descriptions of the cruise route and sights, lots of interesting photographs, wildlife information, Alaska Native Americans, etc.
The included map is very similar to the one you get for free with a Princess cruise book. However, it has more detailed scale (1 inch = 24 miles versus 1 inch = 68 miles). The map is numbered with "mile markers" that correspond to the text in the book.
For more information see <http://www.alaskacruise.com/Books.htm> Be sure to order the Northbound or Southbound edition depending on your cruise plans.