In the cheezy but effective category, if you are trying to create the visual impression of a continuously updated document but don't want the web server to have a bunch of processes loitering for extended periods of time sucking up system resources, you can use a meta tag like

<meta HTTP-EQUIV="REFRESH" CONTENT="15;URL=http://www.myurl.com/myapp?tail=mytail">

If the URL is self-referencing, then the page continuously updates itself every 15 seconds. This strategy is used by the Big Brother monitoring tool, for example. Hope this helps!