I finished my OcTree implementation a few days ago, but forgot to report about it. Please have a look at org.xith3d.scenegraph.OcTreeGroup.
I used it in the Q3FlightBenachmark (optionally). Of course it is not nearly as fast as the BSPTree, but at least makes it 30% faster than simple linear culling in a big group. And it should be a whole lot faster for data, that is more suitable to an OcTree than the shapes in a Q3 level. I could imagine, that even a QuadTree would be better for a Q3 level because of the many slip but high shapes.
The QuadTree will follow very soon. It is a child's play compared to the OcTree and can be easily derived.
Enjoy

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Marvin