The Geek Atlas has been out for a year now, and there's been an iPhone version for a while.
But now there's a special companion application for the book: The Geek Atlas Companion. O'Reilly developed this as a counterpart to the book.
My favorite part of the application is the ability to find places from the book that are near you. The application has all 128 places in it with their coordinates (just like the book) and using the iPhone's GPS it can give you a list of places near you. Each place has a small summary of what you'll see there, but not the complete book text. The application is designed as an add on and not a replacement for the book itself.
A fun part that O'Reilly developed is a quiz based on the book. Multiple choice questions lead you through some of the science that's covered in The Geek Atlas.
Finally, there's a strong community component where users are encouraged to upload their photographs of locations in the book. The application gives rapid access to other people's photographs of the locations.