We apply social network analysis (SNA) to examine the dynamics of leadership in distributed groups, specifically Free/Libre Open Source Software development projects, and its relation to group performance. Based on prior work on leadership in distributed groups, we identify leaders with those who make the highest level of contribution to the group and assess the degree of leadership by measuring centralization of communications. We compare the dynamics of leadership in two FLOSS projects, one more and one less effective. We find that in both projects, centralization was higher in developer-oriented communications venues than in user-oriented venues, suggesting higher degrees of leadership in developer venues. However, we do not find a consistent relation between centralization and effectiveness. We suggest that SNA can instead be useful for identifying interesting periods in the history of the project, e.g., periods where the leadership of the project is in transition.