When I load the Cusom Node template into the text editor and run it in blender I can't add the created nodes in the newly created node tree. I see them but they are grayed out. Is the code somehow deprecated?!
It's not deprecated, it also isn't documented very well yet, expect some trial and error to learn pynodes.
Running the included pynodes template works for me, of note is that switching between nodetree types actually de-selects the active custom nodetree. (Probably worth reporting as a bug)
While I cannot create nodes here, you will notice the new button in place of the node tree name, this may show even if a nodetree exists, it just isn't active.
After making the nodetree active I can add nodes.