Here's some screen shots I took just a while ago.
Also, here's an excerpt from Google System Blog.
Gmail added support for a HTML5 feature that has been recently included in Firefox and Google Chrome: selecting files using drag and drop. If you use Firefox 3.6+ or Chrome 4+, you can now add attachments by dragging the files from your favorite file manager to Gmail. When you drag the files, Gmail shows a drop zone where you need to place the files.
Since I'm using Firefox 3.6, I'm lucky enough to try it. Have a try now!
Sources : CNET and Google System
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