"Other Users" shows all users who are currently logged in. To be logged in currently, one must interact with the www.perlmonks.org (or .com) site in some way within the past few minutes. The list decays with time; if you don't interact with the site, after a period of time, you automatically drop off the list. By "interacting" with the site, I mean browsing the site while logged in, posting to the site, searching, chatting in CB, etc. Pretty much any time your browser hits the PM site, you've interacted, and your presence on the "Other Users" list has been refreshed.

The reason that folks are talking about "Fullpage CB Chat" as a likely culprit for keeping people logged in, is that the "Fullpage CB Chat" works by periodically grabbing updates from the PM XML CB tickertape. That means as long as a user has Fullpage CB Chat running, he will always have a fresh listing on "Other Users".