IQ is renormalized to the bell curve by definition, so multiplying it by 10 isn't guaranteed to be a meaningful operation. And since we have no other way to measure intelligence, it's not clear what Carrier meant by "10 times smarter". For some easy interpretations (e.g. 10x serial speed or 10x parallelism) his claim seems trivially wrong.
Well, central limit theorem says it's mostly a bell curve among humans (you could make a case for a bigger tail on the low end, but still mostly a bell curve). And you can always identify "0" with a random number generator. So multiplying by 10 seems okay to me.
Recently I stumbled upon Richard Carrier's essay "Are We Doomed" (June 5, 2009), when asked to comment about the Singularity, said the following:
What do you think?