I'm using OpenACS 4 with Suse 7.X/Debian, PostgreSQL 7.1.3 (built from source) and AOLserver 3.3.1-ad13 (also from source). Basically the postgres and AOLserver versions are required from OpenACS and I find Suse and Debian the least troubesome Linux Distro's out there.
The latest qmail version is 1.03 (released around '98~99) using daemontools/tcpserver (using http://www.lifewithqmail.org as my setup model). DJB's software is always rock-solid which as the benefit of -not- having to be updated all the time.