Default Users/Groups

[Vlad]

Anyone know exactly what users/groups are required for what services/programs? I'd like to clean up anything that's not needed (ie, apache, postgres). A simple run down of which users/groups are used/required by which programs would suffice. Needless to say, I know that users such as apache are useless unless I have apache installed. Anyone got a rundown of what's needed and what's not? Thanks!