I'm hoping to get away from PHP in favor of mod_python, but the first thing I needed to do was get mod_python successfully working on Mac OS X. I tried once before, using the built-in Apache and Python binaries that ship with Mac OS X. At the time (I think this was still 10.4, but it could have been 10.3), the built-in Python wasn't multithreaded (or something like that) and the mod_python developers were starting to move away from Apache 1.3 altogether.
I had success recently compiling mod_python on Mac OS X Server, against the distributed (but inactive) Apache 2 installation in /opt. However, I found OS X Server to be basically garbage, so I did a fresh install of the client version of Mac OS X, and set about getting Apache 2 to compile, and then mod_python.
It was not easy.