To second Martin Schemmer, it looks like there is indeed something wrong
with threads, probably since 2.6.10-rc1-mm4.
Apache 2 with the worker (threaded) MPM and NPTL is freezing after some
time with 2.6.10-rc1-mm5 and -mm4. This didn't happen with previous kernels.
I'm currently trying to revert various patches to find the culprit.
Best regards,
-Frank.