Clients can see the IP of their website in the website settings when a) the administrator selecetd the Ip in the site settings during site createion or b) when you assign this IP to your customers under System > server IP.
And also i am trying to find out if there is a timeout for the site to logout if some one logged in and there is no activity. And i must say that ISPConfig is a great tool. But i thought these are attractive features for me.
The system keeps the session open until the browser is closed by pinging the server from time to time.