Jon Udell just posted an article about GMail, where he says:
Because Gmail’s behavior is embedded in the UI engine, all subsequent interaction between the browser and the Gmail service is just an exchange of data. What Hwang calls the DataPack format is not XML, though; it’s JavaScript. When you make a request to the Gmail service, whether to refresh your inbox or to modify the list of labels you can attach to messages, the response is a minimal set of JavaScript function calls and associated data objects that the engine uses to update the display.
This is the very first thing that I noticed about GMail, and it continues to amaze me whenever I use it. I have to imagine that the GMail architecture is extremely scalable.
