Serendipity is the property of finding useful things not asked or sought for. Federated Wiki generates serendipity through neighborhood namespace collisions.
As an example, suppose that I write that Wikipedia's production curve is a Logistic Curve, and post it in a small federated wiki on the nature of Wikipedia.
Somewhere else in my neighborhood someone else notes on a page titled Logistic Curve that valuations of social media firms often rely on logistic growth models. It shows up as a twin.
This can be seen as error: quite clearly these are two different uses of the page. They are not revisions at all.
But it can also be seen as serendipitous, bringing me more perspective on my Wikipedia investigation.
Likewise, a third person arriving might write a definition of Logistic Curve for a math class -- and find there are two great examples to use in her neighborhood.
Up until March 2007, many people believed Wikipedia's growth to be exponential. Changes in the rate of growth has prompted a re-evaluation of that, and the current belief is that Wikipedia's growth fits a logisitic-linear growth model.