In Rick Steves' Guidebooks like Barcelona for example, he states that with this book you can save 5% off of the price if you show this book. Does this mean I have to bring the entire Barcelona book to get the 5% off or do I just mention it when I reserve the hotel or motel?
In my experience with 2 or 3 such places, they all wanted to see the book. But they all did give the discount.
Like Steve, I mention it over the phone, and I've gotten the discount sometimes. However, I ALWAYS have the book in my hand (or on the counter!) while I'm checking in, since some places will give you a discount even if Rick doesn't say so. I learned this in the Cotswolds and it has worked for me in several other countries as well.
Xerox or tear out the page for the particular hotel where you're staying. If you had planned to pay w/ a banckcard, ask about a cash discount.