DnD to and from the host OS was what finally got me to abandon Thunderbird for 100% Gmail.

Now if they can just get the clipboard support to work a little better so you can do things like copy a region of the screen and past into an HTML app. It doesn't quite work yet.

These slides are a great distillation of and addition to the HTML5 Rocks Native HTML5 Drag and Drop tutorial[1]. Nicely done.

[1] http://www.html5rocks.com/en/tutorials/dnd/basics

Every day I think to myself that I should drop what I am doing and dive into HTML5.