Social activities such as collaborative work and group negotiation can be an essential part of information seeking processes. However, they are not sufficiently supported by today’s information systems as they focus on individual users working with PCs. Reality-based UIs with their increased emphasis on social, tangible, and surface computing have the potential to tackle this problem. By blending characteristics of real-world interaction and social qualities with the advantages of virtual computer systems, they inherently change the possibilities for collaboration, but until now this phenomenon has not been explored sufficiently. Therefore, this paper presents an experimental user study that aims at clarifying the impact such reality-based UIs and its characteristics have on collaborative information seeking processes. Two different UIs have been developed for the purpose of this study. One is based on an interactive multi-touch tabletop in combination with on-screen tangibles, therefore qualifying as a reality-based UI, while the other interface uses three synchronized PCs each controlled by keyboard and mouse. A comparative user study with 75 participants in groups of three was carried out to observe fundamental information seeking tasks for co-located collaboration. The study shows essential differences of emerging group behavior, especially in terms of role perception and seeking strategies depending on the two different UIs.