Digital libraries, e-journal platforms, portals, e-prints and other web-based information systems provide services supporting users to perform intense work tasks that require complex interaction activities. The main components of such services are the users, the offered content and the system on which they are performed. This paper presents a model, which analyses the attributes of the electronic information services' components that affect user interaction and correlates them in the usefulness and usability evaluation process. An experimental study traces the relations between usefulness and usability, indicating that these evaluation parameters are interconnected and users do not find discriminating differences between them. The analysis of the content and system attributes suggests that user interaction is affected equally by content and system characteristics. Finally, the study illustrates users' preference for the attributes that constitute a useful system in contrast to those that support usability.