I wouldn't say that mod_perl being single-threaded on NT is "buried". It's frequently discussed on the mailing list. The mod_perl documentation describes the Win32 support as "alpha". If it isn't prominently displayed in the documentation, it's probably because NT support is fairly new, and most of us don't expect anyone doing serious performance-oriented mod_perl work to be working on Win32. You could submit a documentation patch to warn people about it if you think it comes as a big surprise to people.