Gmail team has just rolled out a new feature of adding attachment in gmail messages just by dragging and dropping files inside the gmail interface from the explorer window. However this feature is right now supported in chrome and firefox only, but the support is coming soon for other browsers as well.
This new feature is really going to save good amount of time while sending a mail, when was spent in location the files buried under deep directory structure. I have just tested this feature in my gmail, looks like it has been rolled out for all the gmail users, you can check the same in your gmail inbox.
Note: Make sure that you drag a file in the subject box or some where near it.
[ Source – Official Gmail Blog ]