Many claims have been made about the problems caused by not documenting design rationale. The general perception is that designers and architects usually do not fully understand the critical role of systematic use and capture of design rationale. However, there is to date little empirical evidence available on what design rationale mean to practitioners, how valuable they consider them, and how they use and document design rationale during the design process. This paper reports an empirical study that surveyed practitioners to probe their perception of the value of design rationale and how they use and document background knowledge related to their design decisions. Based on eighty-one valid responses, this study has discovered that practitioners recognize the importance of documenting design rationale and frequently use them to reason about their design choices. However, they have indicated barriers to the use and documentation of design rationale. Based on the findings, we conclude that much research is needed to develop methodology and tool support for design rationale capture and usage. Furthermore, we put forward some research questions that would benefit from further investigation into design rationale in order to support practice in industry.