Whatever happened to Mastery Learning?

I have been reading "Schools, Society and Mastery Learning" (Block, 1974) with the intention of reconnecting with some of the theory behind e-learning. Looking across different educational areas now, I see fragments of the Mastery model in use, and frequently in misuse. What I do not see is either its consistent application or a coherent critique.

Can anyone help me with pointers to either
- Mastery principles being consciously used in e-learning now, or
- specific criticisms or rejection of Mastery principles in the context of e-Learning

I hope to pull this together into a blog post, and will of course credit all sources.