>> Interestingly, I have a second--virtually identical--server that I
>> just tried initdb on. FreeBSD 8.3-RELEASE-p5, postgresql-server-9.2.2.
>> Exact same "FATAL: could not open file pg_xlog" error. So it is
>> reproducible.
>
> Does virtually identical extend to architecture, amd64?
Yes... and hardware. They only vary in the amount of CPU cache--one
has twice the other.