Last week, the Wall Street Journal introduced me to a new web-technology term: Ajax. I'd link you to the story, but of course it ain't free. Fortunately, Adaptive Path, who coined the term, has an excellent overview: "Ajax: A New Approach to Web Applications."
From a user's standpoint, I have to say that Ajax has been put to glorious good use at such places as Google Maps: sites that serve dynamic content without reloading the page.
I'll save more detailed comment about Ajax for those more knowledgable. But I can't resist passing along my favorite question and answer from the Q&A section of the Adaptive Path introduction:
Q. Are Ajax applications easier to develop than traditional web applications?The understatement of that "not necessarily" is perfect. Posted by Jon on March 21, 2005 10:42 AMA. Not necessarily. Ajax applications inevitably involve running complex JavaScript code on the client. Making that complex code efficient and bug-free is not a task to be taken lightly, and better development tools and frameworks will be needed to help us meet that challenge.