Interesting article; and Motl's a well-known knowledgeable and sometimes correct debunker. I didn't disagree substantially with anything up until here:

It was the probability density for a brain creation itself, around exp(-10^{57}), that determined the "importance" of the effect of a spontaneous brain creation. If we multiply this small number by a huge volume, we obtain a huge result that has no physical relevance for any place of the Universe in the present, past, or future (because the factor of the "spacetime volume" transformed the quantity into some "statistics of events in the whole spacetime" i.e. a global quantity which can't possibly influence any observable phenomena in a region of spacetime, by locality and causality).

I'm not exactly sure what he means, but it seems like even if the brains are not local to anything else, they are the observers; so the objection seems moot.