Wikipedia has been a resounding success story as a collaborative system with a low cost of online participation.

However, it is an open question whether the success of Wikipedia results from a "wisdom of crowds" type of effect in which a large number of people each make a small number of edits, or whether it is driven by a core group of "elite" users who do the lion's share of the work.

In this study we examined how the influence of "elite" vs. "common" users changed over time in Wikipedia.

The results suggest that although Wikipedia was driven by the influence of "elite" users early on, more recently there has been a dramatic shift in workload to the "common" user. We also show the same shift in del.icio.us, a very different type of social collaborative knowledge system.

We discuss how these results mirror the dynamics found in more traditional social collectives, and how they can influence the design of new collaborative knowledge systems.