My own experience. I coded async DHTML back in 2002, with iframes or async XML loading (since 2005 named AJAX). I debugged GMail back then (the first version with the blue rounded corners, the same design as Google Groups and Google Code)
It's incredible hard to find older web resources from 10 to 15 years ago, as most bookmarks don't work anymore. And some current websites sadly try to rewrite the history.
Both GMail (2004) and Google Maps (2005) used iframes for the first years. There were still many users with older browsers without real AJAX support - Firebird/Firefox/Mozilla Suite/Netscape, Safari(?) and some Opera. Only IE 4/5+ and current Firefox/Mozilla browser supported real "AJAX" in late 2004. Iframes were supported by most browsers.
It's incredible hard to find older web resources from 10 to 15 years ago, as most bookmarks don't work anymore. And some current websites sadly try to rewrite the history.
e.g. Aaron mentioned it: http://www.aaronsw.com/weblog/ajaxhistory and you can search through Slashdot.org, (former) digg.com and web.archive.org
Both GMail (2004) and Google Maps (2005) used iframes for the first years. There were still many users with older browsers without real AJAX support - Firebird/Firefox/Mozilla Suite/Netscape, Safari(?) and some Opera. Only IE 4/5+ and current Firefox/Mozilla browser supported real "AJAX" in late 2004. Iframes were supported by most browsers.