Rosalind - 10:26 am on Jun 7, 2013 (gmt 0)
What he doesn't go into is topic-specific authority. Most good writers stick to a few topics, and that's what makes them good. I want to read Danny Sullivan's take on SEO, for instance, but not necessarily on ornithology or crafting tips (unless he happens to have hidden talents in these areas).
So there are two aspects to this. There's the talent of authorship in terms of writing clear, grammatical text that people enjoy reading; and there's the importance of expertise in a subject area. Both are the kind of things searchers will be looking for, but I can see Google struggling to understand the latter. If they can nail that, in a way that Klout really haven't yet, it will make rel=author worthwhile for all concerned.