This study compared users' self-reported and observed usability problems within a Web-based information system, based on their experiences with the system. Eighteen employees of a company which created the system were chosen to represent typical end-users. Each participant was asked to complete a specific list of tasks within the system, after which he or she answered several questions regarding the system's usability. While advanced users generally completed the tasks in less time than novices, the number of tasks completed correctly and the number of usability problems reported did not differ significantly by experience level. Problems identified by the participants reflected accepted usability guidelines, suggesting that, by following user-centered design principles, such problems can be avoided in future development efforts.