I got the following email this morning that astounded me.  I thought I'd share (with the author's permission):

Just dropping a line telling you I like your WPF Unleashed book a lot, and brought it to my recent trip to Tibet. I also took a picture of your book in the wild, and thought you might like the photo! 

Cheers,
Luc (Paris, France)

Looking through the photo album, I uncovered this photo as well.  I guess the book can be used for many things!