Software visualization is nifty stuff; but is it the powerful cognitive tool it is often assumed to be? This chapter attempts to moderate the understandable enthusiasm for software visualization and to raise some of the questions for which the discipline doesn't yet have answers. The chapter is structured as a list of questions with discussion. The questions are not a comprehensive analysis of cognitive challenges in software visualization. Rather, the chapter attempts to provide a list sufficiently provocative to give designers pause, in order: (a) to establish that good software visualization isn't simply a matter of mimicking paper-based tasks or doing what is technically easy---and certainly isn't `solved' yet; but also (b) even simple tools can improve software comprehension, if they're the right ones.