This paper describes a method for studying idioms-based implementations of crosscutting concerns, and our experiences with it in the context of a real-world, large-scale embedded software system. In particular, we analyse a seemingly simple concern, tracing, and show that it exhibits significant variability, despite the use of a prescribed idiom. We discuss the consequences of this variability in terms of how aspect-oriented software development techniques could help prevent it, how it paralyses (automated) migration efforts, and which aspect language features are required in order to obtain precise and concise aspects. Additionally, we elaborate on the representativeness of our results and on the usefulness of our proposed method. Preprint accepted for publication in: Sixth International Conference on Aspect-Oriented Software Development, Vancouver, Canada, March 12-16, 2007