I can't get this wood to work, everything is just turning black :-/ it looks OK-ish in the preview, but my object is black.

Same here, as far as i can tell the material does not repeat itself but instead it ends at some point leaving just some piece of the object with the wood and the rest in black. I tested it both with my version and the source file and neither of them worked.

Try putting a color ramp after all the texture nodes. It should cap it. It worked for me.