Yes, I wonder whether you could use this as an extra emphasis effect for certain buttons on a page, have the important buttons (sign up, buy, etc.) with depth,

Yes, I wonder whether you could use this as an extra emphasis effect for certain buttons on a page, have the important buttons (sign up, buy, etc.) with depth, and the less important - but still necessary - just flat. Would be interesting to A/B test. Having thought about it, a fair few websites already do this with certain confirmation dialogues. eg. They have the primary button with a prominant graphical style and the cancellation option as just a small standard html link.