Most Web-based chat applications, such as washingtonpost.com's Live Online chats, use
meta auto-refresh tags to give the illusion of continual updating. Those are easy to implement (a single line of code in your page will do the trick), but they carry major baggage: Every time the page refreshes, the browser must reload the entire page from scratch. Of course, in a chat setting, user-generated content doesn't change; rather, more content keeps being generated. In other words, it's redundant to reload an entire chat if you know none of the text has changed; it's much more efficient to load only the newest stuff.
The first chat we've got scheduled is Wednesday (today) at 3:30 PM U.S. Central Time. The chat guests are four of the Women of KU (a group of calendar models that our Web site sponsors). Should be an interesting conversation. Check it out, if you've got a chance. It'll be linked off of kusports.com.