AJAX is being overused for some really simple and silly stuff. Most of it doesn't really matter - you could just as easily do it with a new web page. But there's one application they've never been able to do quite right with web pages - and that's chat or instant messaging. Every page refresh (which is every few seconds) loads a new page. It looks horrible. Nobody likes to use it. It'll sometimes refresh while you're typing something, losing what you typed - unless it is set up with two windows open. No matter how you do it, it looks and works horrible.

But AJAX is the perfect solution for chat. All the data is being refreshed in the background - and the page doesn't have to be reloaded - until you sign off. It's the killer app for AJAX.

I've glanced at a few open source AJAX chat packages - most of them are really, really primitive. So far I've only found one that looks promising. But open source isn't the only source out there. It only takes a couple of hours to write all the skeleton code. You're going to see chat on pretty much every major social web site soon. It can also be integrated pretty quickly into any of the leading IM applications. The interesting thing is that It can be integrated into any web page. I could have chat running on this page, for instance.  I don't know that I'll end up doing so. I'm really not fond of chat. I'm just alerting you to the possibilities... 

Oh, and with the ability to do things interactively without the annoying flicker of page reloads, you're going to see a whole lot of AJAX games pretty soon. I mean really. Games make up a huge chunk of the digital economy. But if you're looking for games online, seems like there's only one - Texas Hold'em. You can't even find a decent game of chess online. 

The other killer app for AJAX is search. Coincidentally I'm looking for employment and the search companies seem to be the ones with openings... Of course they've probably already set people loose exploring possibilities. But picture this - you've got back 2,000,000 results on your search term. Hmmm... What if you could just hover your mouse anywhere on the page and have the result set refined in real time based on the word or entry you're hovering over?  Let's use the keys example. Locksmiths, Florida Keys. Encryption keys. Alicia Keys. You want to take a vacation and typed 'keys'. Hover the cursor over the word Florida for a couple of seconds and all of a sudden you're looking at just Florida Keys and down to half a million results. Now hover over the word hotels. ...The Hilton. ...Reservations. Pretty soon (10-20 seconds) you're down to a few pages of possible results matching precisely what you're looking for and you haven't clicked anything.

See what I mean? There is absolutely nothing preventing this web application from being available to you tomorrow. The technology to do this exists today; and in fact has existed for several years - it's JASMOP (Just A Simple Matter Of Programming).