HTTP session expiration

Tomáš Zvěřina outlines a way to warn users
 when their session is about to end. In his example, a client-side script displays a warning
 five minutes before the session expires.

To be honest, there are a few things I don't like about this approach. It's a matter
 of how it feels to the user. For instance, what will someone do when they see 
 “You'll be logged out in five minutes”? Might they think they need to log back in 
 to the operating system?

I prefer to make it clear to users what's happening when a session expires. I like
 returning a page that tells the user the session has ended. Instead of a standard
 500 error page, it gives them a way back to the starting point 
 of the application or suite of applications. If you have the time, leave a comment. 
 I'd love to hear how you handle this.