Many file managers (like Nautilus, Windows-Explorer, ...) implement this: If you drag files/folders in the list or icon view to some place in their own directory by using the right or middle mouse button, you can select if you want to make a copy or a (sym)link to that files/folders when you release the mouse button. As the result a copy/link of the selected items is created in the same directory, with a string like "(Copy") attached to the original file name. Since this can be very useful sometimes, I would love to see this feature in Thunar ;-)
It is already available in Thunar, just select the folder and press Ctrl+C followed by Ctrl+V, or Edit->Duplicate. For symlinks, use Edit->Make Link. Thunar does not use this with Drag'n'Drop, because it's usually too easy to accidently duplicate files/folders (the typical windows user has atleast one "Kopie von XXX" or "Verknüpfung mit YYY" and doesn't know what it is nor where it comes from). Also it would make it difficult to cancel drags.
Oh sorry, I have to admit that I obviously didn't pay much attention to the Edit-menu. Then this was even solved before I asked, very nice :-)