I actually edited my w3t so it doesn't save your cookies and you have to log in everytime. I had several complaints from users who had two accounts and used the same computer (husband and wife / brother and sister / etc) that they'd log in under the other person's name and then when they hit logout and tried to login under their own name w3t would say "Hello, their name" in the corner but the main part of the page would say they're not logged in. At that point neither account could log in so I had to make a little script to clear all cookies from my server in the w3t folder and close all browser windows and then they'd hafta try and relogon and sometimes that didn't even work and I'd hafta explain to these people how to manually delete the cookie from their browser folder. So I just made all my cookies in w3t temp cookies and that fixed the problem.
