The Uncanny Valley of User Interface Design: Why web apps shouldn't look like desktop apps
radar.oreilly.com
radar.oreilly.com
Gmail uses Ajax to accelerate common operations (e.g. email address auto-complete) and to enable data transfer sans jarring page refresh (e.g. refresh Inbox contents) but its core look and feel remains very similar to that of a traditional web page. In my view, this is not a shortcoming; it's a smart design decision.
This isn't to say that 'web'-style interfaces don't have room for improvement, but it's a different ballgame than the desktop. On the web we have load time concerns, a different toolset for building the interface, and different considerations in terms of color and space.
Not to mention the precedents set by every other web page that has come before which people are used to. Geez, we have to do a scriptaculous hilite on every xhr just so people will notice what's going on.