Perhaps the most useful thing to offer with AJAX is some sort of UI cue that the application is doing something. For example: double click a conversation, and there's about a 2 second delay before the email view displays. There's no visual cue that anything has happened because of my click. I'd say at the very least the cursor should be hourglassed; at best, the conversation view should also be blanked, and replaced with a "loading" screen. It'll make the app appear much snappier. This applies to pretty much all the AJAX calls....