© 2014 Springer International Publishing Switzerland. All rights are reserved. When new user interfaces or information visualization schemes are developed for complex information processing systems, it is not readily clear how much they do, in fact, support and improve users' understanding and use of such systems. Is a new interface better than an older one? In what respect, and in which situations? To provide answers to such questions, user testing schemes are employed. This chapter reports on a range of risks pertaining to the design and implementation of user interfaces in general, and to newly emerging interfaces (3-dimensionally, immersive, mobile) in particular.