first it was gmail. then it was google maps. now it is google suggest & now there are lots of web application architects moving themselves ajax way. asynchronous javascript xml (ajax) engine is nothing much but a javascript layer behind your web ui, that talks to the server (for the data to be rendered). well, this kind of thing has been around for a long, but now with google adopting this in one of their flagship products, its being well recieved by the community. Chris , a fellow blogger did a thorough dissection of google suggest service.
the way it works at the core is, the javascript layer (hidden somewhere on your web ui) is responsible for fetching data from the server using XmlHTTP object. Since the main html components are not doing the data fetch, the page doesnt do a refresh between client <--> server data fetch cycles.
what can this be used for? lots! for starters you can build a powerful autocomplete / filter connected to your database and driven by a web ui. all this without a page refresh in your web ui!
will post more with examples when i have the code reformatted to post here…..