Here is an example of a default Lyris configuration with the List-Unsubscribe header. Lyris really implemented this well (not surprising since I was working very closely at the time with John Buckman, founder of Lyris).
Not only does Lyris use VERP (notice the numbered codes in the List-Unsubscribe URL) but they also make the List-Unsubscribe header a default on new lists. Administrators can easily turn on the rest of the RFC 2369 headers (List-Info, List-Subscribe, List-Help, etc.) with one click.
From: [email protected]
Date: August 30, 2006 3:22:22 PM CDT
To: Joshua Baer <[email protected]>
Subject: Cavenders.com - Labor Day Sale!
Return-Path: <[email protected]>
List-Unsubscribe: <mailto:[email protected]>