Drag and drop: better visualization to discern between copying, moving, linking
When one grabs an icon (file) with the LMB (left mouse button) and drags it to another location or surface, the file is moved or copied depending on it's location, after the user lets go of the mouse it can be seen that the file has been copied (the file is still in its orinal location and in the new location) or has been moved (the file has disapeared from its orinal location).
Therefore I suggest to add the following visualization differences:
When the default action is copying: the icon in the original location should stay and a transparent copy should be held on to the mouse cursor until the mouse button is released
When the default action is moving: the icon in the original location should be moved away from the original location and held on to the mouse cursor until the mouse button is released, the icon held on the mouse cursor should be much less transparent (more opaque) then when it is being copied)
The default drag-and-drop-with-LMB action could be set to always copy, move, or link. When the default action is linking a process visually similar to the copy action takes place with the addition of a dashed line (similar like the dashed lines in a selection rectangle) following the icon held by the mouse cursor. This visual 'dashed-line-link' behaviour could be displayed briefly during linking with the RMB (right mouse button), say 200-500ms.

Comments
Re: Drag and drop: better visualization to discern between copy
I like this idea. I think you should also be able to select the action while dragging by pressing a key - maybe "m" to move instead of copy (if copy is default).
One thing I'd really like to see is "right-left-click cancels drag". This was a feature on Amiga which I've never seen anywhere else. Say you're dragging something and you change your mind (or got the wrong one). You should be able to cancel the drag instantly by hitting right mousebutton. Currently on most operating systems, you can't cancel a drag and you have to carefully put back the item.
Re: Drag and drop: better visualization to discern between copy
Personally, a symbol-overlayed mouse cursor (like a +/arrow/chain for copy/move/link) would be sufficient. Different transparencies aren't intuitive and while it sounds cool to have a chain trailing the mouse cursor, it could be awkward when changing workspaces.
@M.Evans (I'm not stalking, I swear :) )
It's not a bad idea, but I don't think 100% consistent. I'd prefer, if I started a drag with the LMB and while dragging changed to the RMB, the standard action of the RMB would happen: the context menu letting me copy/move/link/cancel.
IMO the single best "Oh my gods, what am I doing?! Make it stop!" panic button is the ESC key.
Re: Drag and drop: better visualization to discern between copy
well having used the ROX desktop before which is modeled a bit after amiga and the context menu with copy link move cancel is highly ideal you just drag it and it asks
I like the right click to cancel as well I have often started a long copy say a couple Gb or so when i really wanted to move etc....
Re: Drag and drop: better visualization to discern between copy
IMO the single best "Oh my gods, what am I doing?! Make it stop!" panic button is the ESC key.
I don't mind having the ESC key cancel the drag, as long as something cancels it. I thought right mousebutton would be better because you don't have to reach for the keyboard. I can see the conflict with right mousebutton = context menu though. (damn those context menus ;)
Re: Drag and drop: better visualization to discern between copy
I have changed my mind about the visualizations during dragging because I realized the system cannot know before hand what the user is going to do because you could drop any object onto any other object not just a Tracker window.