I suspect this is not really feasible given the way drag-n-drop works, but here
goes :

I'd like to be able to drag a window from another workspace in the workspace
switcher applet, and drop it in the main screen area (ie outside the panel,
where all the other windows are), in order to drag it to the current workspace.

Rationale :
* the dropping zone is almost infinite, hence it's much easier and faster than
dropping on the small "current workspace" square of the workspace switcher.
* As the "current workspace" square represents the main screen area, it makes
sense that both would behave the same.
* I just did it without thinking, so it must have some kind of instinctive
consistency :-)

But then again, I don't know if it can be done at all.