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I'm currently working hard to build a drag and drop support to core Vaadin.
While waiting for 6.3 release, you can enjoy the future of web with VaadinDropZone component. I extracted it from my prototypes and made it 6.2 compatible. It receives data to server side component via HTML5 style drag and drop process. HTML5 drag and drop combined with the File API (available in just released FF 3.6) one can drop even files to Vaadin application. The example application shows png images if you drop them over the "drop zone".
The current version supports just text data flavor + file contents for FF 3.6. If should be quite easy to extend though.