Usability testing need not be formal or expensive, but it should be iterative and happening all the time. Given the complexity of serving up contemporarily digital resources and services, changes need to be incremental and continually refined. Tweaking rather than turnkey. So how do you tweak? Using guerilla usability. Specific attention will be given to guerilla (informal) usability testing of traditional digital interfaces (desktop- and laptop-based) as well as new types of interfaces (gestural and mobile). Attendees will leave with an overview of, and framework for, designing and implementing extremely low-cost usability tests of digital resources and services.