In recent years, many desktop applications have been ported to the world wide web in order to reduce (multiplatform) development, distribution and maintenance costs. However, there is little data concerning the usability of web applications, and the impact of their usability on the total cost of developing and using such applications. In this paper we present a comparison of web and desktop applications from the usability point of view. The comparison is based on an empirical study that investigates the performance of a group of users on two calendaring applications: Yahoo!Calendar and Microsoft Calendar. The study shows that in the case of web applications the performance of the users is significantly reduced, mainly because of the restricted interaction mechanisms provided by current web browsers.