Flow visualizations/sankey diagrams like Google Analytics?

[harald]

In December Google Analytics rolled out an amazing feature they call
"visitors flow", flow diagrams to track where users come from and
where they are leaving.

Screenshot:
http://yfrog.com/klhrnyp

I'm not quite sure what's the exact name for this kind of
visualization, it looks like a discrete kind of alluvial diagram, or a
sankey diagram without feedback-loops. The data being visualized, may
be described as graph data (not time series as in ordinary alluvial
diagrams) with a numeric vector indicating the strength of the flow.

Have anyone tried to make this kind of flow visualization using
InfoVis?
If not, are there any other JS libraries with working demos of it?



References:

Sankey Diagrams and Flow: Over A Hundred Years of Innovation
http://analytics.blogspot.com/2011/12/sankey-diagrams-and-flow-over-hundred.html

Alluvial diagrams are a type of flow diagram originally developed to
represent changes in network structure over time:
http://en.wikipedia.org/wiki/Alluvial_diagram

Sankey diagrams are a specific type of flow diagram, in which the
width of the arrows is shown proportionally to the flow quantity. They
are typically used to visualize energy or material or cost transfers
between processes
http://en.wikipedia.org/wiki/Sankey_diagram