Memory
For anyone concerned about Kowari tests failing on the Mac, I've just been able to confirm that it's my fault, not Kowari's. It seems that I may have some intermittently faulty memory.

Yay.

Hopefully it is my memory expansion module, and not the built-in RAM. When I have some time this weekend, I'll try taking the extra RAM out and doing another build. Hopefully it will pass, indicating a problem with the memory expansion. Fortunately, everything is under warranty, but I'd rather be without memory for a few days than without the whole computer while it gets fixed.

This may also explain why the system crashed last weekend.