  We develop a new approach to the study of the dynamics of link utilization in
complex networks using records of communication in a large social network.
Counter to the perspective that nodes have particular roles, we find roles
change dramatically from day to day. "Local hubs" have a power law degree
distribution over time, with no characteristic degree value. Our results imply
a significant reinterpretation of the concept of node centrality in complex
networks, and among other conclusions suggest that interventions targeting hubs
will have significantly less effect than previously thought.
