The hackathon was hosted by Streamy.
And the resulting extension is hosted on GitHub as the Cascading.HBase project.
It currently compiles fine with HBase trunk, but as users start to bang on it, I suspect some features will leak into the API it is binding to so that it behaves a little more robustly in a production HBase and Hadoop cluster.
There is also a wiki page over on the HBase project site with a small example: HBase/Cascading.
For a more detailed examples, watch the HBaseTest unit tests as they evolve.