The new Spotlight search in Mac OS X Tiger shows what a search engine should not have: a submit button. Why do applications force us to click on a button, instead of showing us what we are looking for as we type?
The widespread deployment of browsers supporting the XMLHttpRequest object coupled with an increase in processing power on the server side enable us to create web applications that feel more like Spotlight. It is in fact my belief that there will be a move towards this type of interaction in the coming years, starting with getting rid the submit button.
Updated (2005-04-28): C�dric Savarese asked people in his blog for suggestions of applications that would need an Ajax makeover. What we did with Translate This is an example. You have a suggestion? Post it in C�dric's blog.