example: Go to your Facebook wall, scroll the end of the page, Facebook will load more wall posts asynchronously. Or just click on an images in your wall post. The image dialog (with comments and larger image) is loading asynchronously as well. (You can see the GET requests with firebug).
But by looking and the firefox tab, you see the loading indicator, just like when a postback occurs.
I know this can be achieved by using an IFrame and changing its src. Just like what iGoogle does. But I’m not sure if Facebook uses an IFrame to load additional wall posts. Is there another way to achieve this?
Update: by saying "loading indicator" I did not mean an ajax indicator.
As I mentioned the browser indicator (the one at the laft side of a tab showing us if the page is loading) changes to loading like it is a postback.
Not AFAIK.
My guess is they probably set the IFrame src to an ajax method and when loaded, they move the content to a div (or another element).