Why not use the userstamp plugin? It extends AR the same way ActiveRecord::Timestamp does. Works for me.
script/plugin install http://www.delynnberry.com/svn/code/rails/plugins/userstamp
Im also using this, it work pretty good for me, except I don't like how you have to define this in every model:
belongs_to :updated_by, :class_name => "User", :foreign_key => "updated_by" belongs_to :created_by, :class_name => "User", :foreign_key => "created_by"
It does work pretty reliably for me tho. If there were a way to just have it work like timestamping with no configuration beyond if the database field existed, I always thought that seemed like the most ideal solution. Good luck. I'm curious to see what you decide in the end. ~michael