This is for those who have the map permanently bound in the book. Oh noes!
Tools required: X-acto knife (or similarly sharp and precise cutting utensil), piece of cardboard, pencil.
1.) Fold out the map (as much as you can). This should leave the short side still attached to the book.
2.) Using the straight edge of the cardboard and a pencil, draw a cutting guideline.
3.) Place cardboard underneath the map and directly against the spine of the book. This should elevate the map enough so that it does not touch the last page of the book.
4.) With the knife, carefully follow your guideline to remove the map from the book. Slower is better - it makes a cleaner cut!
Fortunately, the edge that is bound to the book does not have any important text close to its edges. Hope this helps somebody out!
Look here on the product page for pictures of Jeff and Josh doing just about the same thing as Lilith suggests above.
Just some advice to be very careful on the pressure cutting the map out. I even used a heavier cardstock than the recommended file folder, and the blade was able to cut through that without much pressure behind it. And once through the protection, the paper beneath will get cut. I cut through 2-3 pages in the back and didn't even notice the blade was going through the cardstock (I used a new razor since I wanted a clean cut).
Just a head's up to be careful with those sharp blades and avoid my own mistakes.