Matters

The Fishbowl: The New Web UI: "The first prominent use of XmlHttpRequest that I encountered (in my admittedly limited range of web browsing) was in the once exclusive but now culturally irrelevant Google social side project, Orkut. After this experiment, though, the technique really fell into place with GMail.
If you are a web developer, even if you don�t need any more mail space, get a GMail account now. In one blow, Google�s engineers massively raised the bar on what we should accept from a webapp. Here�s a highly regarded, mainstream application that is responsive, with a dynamic UI and even comprehensive keyboard navigation, but that still feels like a web application."