This study aims to investigate the effectiveness of Scatter/Gather browsing for information retrieval. We conduct a within-subject study of 24 subjects, in which each user conducts searches on a Scatter/Gather system and a classic web search system, and provides feedback and comments. Eleven out of twenty four subjects consider that Scatter/Gather system helps them complete the tasks more effectively as it sorts the results and filters out useless information. We discuss strengths and weaknesses of Scatter/Gather compared to a classic web search interface and examine influences of topic characteristics on Scatter/Gather effectiveness. It is suggested that topic familiarity and specificity have significantly influences on several categories of user perceived retrieval effectiveness. The influences appear to be greater with the Scatter/Gather system. We find that viewing time has a moderate positive correlation with relevance and usefulness of a web page, which are highly correlated to each other.