We have just enhanced PresentationServer adding an automatic loading indicator. PresentationServer gives you an Ajax XForms engine: you write standard XForms, PresentationServer renders it in an Ajax web page that runs in mainstream browsers.
With XForms, you can implement forms where server-side processing happens as the end-user interacts with the page; feedback is given to the end-user on the same page, without having to reload another page. The instant translation page shows this: a translation of the text you enter is provided as you type.
However, as you interact with the page, it is not always clear when server-side processing is happening. For this reason, if a request takes more than certain number of milliseconds, which you can setup in PresentationServer, a loading indicator will be displayed automatically.
Try it out in the instant translation page.