A lot of people complain about Gmail not having a native application on the iPhone. While it's not clear if Apple will even allow that yet with the new iPhone 3.0 SDK, one thing that is becoming more clear: Soon it won't need one.
The reason is that its iPhone-optimized mobile version continues to get some killer features. The latest is the ability to use the swipe gesture to archive messages — yes, within the browser. Users of the iPhone's native mail app will recognize and appreciate this functionality (though in that app it's used to delete messages, not archive them)