Knowing the program timing characteristics is fundamental to the successful design and execution of real-time systems. A critical timing measure is the worst-case execution time (WCET) of a program. Often, timing analysis??in industry is done by measurements. Recently, tools for deriving WCET estimates have reached the market. With more widespread use of WCET tools in industry, the usability aspects of these tools will be of growing importance. In this paper we discuss usability using the results of the WCET Challenge 2006, which was the first event that compared different WCET tools using the same set of benchmarks. Another source of input to the discussion are experiences from industrial case-studies of WCET tools. Finally, we point out some areas for future research and development for WCET analysis methods and tools.