The last book published by O'Reilly about "Programming Interactivity" shows how to use some of the Libelium's Arduino modules to easily create interactive applications. Their usability and fast integration are two of the concepts remarked by its author (Joshua Noble) as two main features to be taken into account when talking about hardware design and open platforms. More information about the book here:Programming Interactivity A Designer's Guide to Processing, Arduino, and openFrameworks.