Ok, let's talk connotations.
If g is a causal factor then "A has higher g than B" adds additional information to the statement "A scored higher than B on such-and-such tests." It might mean, for instance, that you could look in A's brain and see different structure than in B's brain; it might mean that we would expect A to be better at unrelated, previously untested skills.
If g is not a causal factor, then comments about g don't add any new information; they just sort of summarize or restate. That difference is significant.
A predictive factor is enough for predictive uses, but not for a lot of policy uses, which rely on causality. From your comment, I assume you are not a lefty, and that you think we should be more confident than we are about using IQ to make decisions regarding race. I think that Shalizi's reasoning is likely not irrelevant to making those decisions; it should probably make us more guarded in practice.
The kinds of implications I'm thinking about are that if IQ causes X, (and if IQ is heritable) then we should not seek to change X by social engineering means, because it won't be possible. X could be the distribution of college admittees, firemen, criminals, etc.
Not all policy has to rely on causal factors, of course. And my thinking is a little blurry on these issues in general.
This thread is for the discussion of Less Wrong topics that have not appeared in recent posts. If a discussion gets unwieldy, celebrate by turning it into a top-level post.
Part 2