It would be a great idea to have an AJAX option on the online users module which would update the online users "live". I say "live" because if the option was switched on, it would be up to the admin on how often it was updated. If the server was a busy one, the admin could set the update time lower than on a quieter server.

Still, would be a great option - probably not too tricky to implement - and I'd love to see this included.