[Be el o ge]

For some time already Drag & Drop within the browser is a pretty common feature for web applications. The next step would be Drag & Drop interaction between your desktop and the web application … without using a plugin (Adobe Air, …).

Swell, a Javascript library, seems to be promising: Wouldn’t it be Swell to be able to drag and drop between Web and desktop
Also there is a demo on their web page: Drag and drop files from your desktop to your browser. They say “two browsers are playing well with the demo (Safari 4, Chrome 2+) while others degrades gracefully.”

Now, even cooler would be such support in the Google Web Toolkit, but it seems a common approach there is to utilize Google Gears, which again forces the user to install a plugin (except in Chrome, where Gears is an integrated component). Read more about it here and here.