When hard-to-use computers cause users to become frustrated, it can affect workplace productivity, user mood and interactions with other co-workers. Previous research has examined the frustration that students and their families face in using computers. To learn more about the causes and measure the severity of user frustration with computers in the workplace, we collected modified time diaries from 50 workplace users, who spent an average of 5.1 hours on the computer. In this exploratory research, users reported wasting on average, 42 - 43% of their time on the computer due to frustrating experiences. The largest number of frustrating experiences occurred while using word processors, email and web browsers. The causes of the frustrating experiences, the time lost due to the frustrating experiences, and the effects of the frustrating experiences on the mood of the users are discussed in this paper. Implications for designers, managers, users, information technology staff and policymakers are discussed.