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Aha, got it - Rendering path was set to lagacy vertex lit. Changed it to forward, it's all working now.
Yup, got a light in the scene, supporting 10 pixel lights, DX9 rendering enabled on the shader (I'm testing with the Tiles example shader) and it's still showing up solid black.

In fact, all the shaders in the Example scene, aside from the Custom Lighting + Outline one, show up as solid black too.

I've tried creating an entirely blank project and they work fine in that, so it's presumably got to be something to do with my project's setup. I've recently updated from Unity 4.3 to 5, so I'm wondering if that could have anything to do with it?