Seems like quite a serious issue.

1. Could it be that you have no dynamic lights in your scene, and you aren't baking lightmaps?
2. Which Unity version are you running?
3. Are you 100% sure the material is using the same shader you're working on?

That's very weird :(
If you make a simple diffuse shader then? Plug in a value of 1 into diffuse, disconnect the rest from the main node - will it work?

It does look a bit expensive, but, if you enable GLES as well in the shader settings, does it work on mobile after that, even though it looks black in SF?

It's not as far away as it sounds, I actually have a nearly working implementation. The tricky part is all the caveats :)
And yes, most things in SF is handled on a per-pixel level, while some things are optional. For instance, light probes can be both vert and frag sampled.
But at the moment, SF isn't very mobile aligned, SF is created to push the boundaries of what's possible on the high-end.

Strange. How does your shader tree look? Is OpenGL ES 2.0 enabled in the shader settings?

Not yet! But is is something that's most likely going to be added for 1.0

However, it did show what the issue was :)
The code for the dot product is wrong in the node previews! I'll get this fixed for 0.19!

Why are you doing a dot product between two values, by the way? That's generally used for vectors - you could simply use a multiply node in this case.

That said, the issue remains, and is a weird one. I'll have a look!