I have been playing around with the CustomNodeType template that ships with Blender. I have simplified the code, and attached it in the BLEND file, so the node has only one value, a default_value of a float type. I have modified the poll() function so the node category shows up in the Cycles material menu. I can get my node to appear in the Cycles material node tree but when I connect the value to a known float input it does not work.
For instance, in this image I have a custom node providing the value 0.0 to the roughness of a Glossy shader. The render output should be a perfectly mirrored sphere but instead the Cycles node is ignoring my float input and using the internal roughness value of 1.0 to produce a matte like finish instead.
Does anyone know how to get other node tree types to accept values from custom nodes?