POSIX semaphores should be fixed in 8-CURRENT, pending MFC.

There are rtld + malloc issues in FreeBSD. Python multiprocessing's
use of POSIX threads is not strictly POSIX compliant, as it tries
to do a lot more than just call exec() or async-signal-safe POSIX
APIs after fork()-ing. There is a degree of reluctance in the camp
to fix for these reasons...

In the meantime, you may wish to try building Python 2.6 on FreeBSD
using GNU Pth, here is a patch:

http://people.freebsd.org/~bms/dump/python26-fbsd-pth.patch

thanks!
BMS