What, no snide comments? I'm disappointed :) Good article, I've always thought the microkernel-but-single-server architecture of Darwin was a bit strange, and I'm not surprised it causes performance problems in certain situations.
Here is a comparison of low-level benchmarks between Linux and OS X on identical Mac hardware; the results are similar with Linux being faster in most cases. Of course, this isn't terribly relevant for the large majority of applications.