It is a small challenge to understand, what drag* icon action does copy or move in Leopard.

1) Dragging from one folder to another on the same disk moves the icon.
2) Dragging from one disk to another copies the folder or the file.
3) It is possible to hold option key [alt in Windows terminology], while dragging folder or file to copy it. Vice versa apple key is used to move the file.
* Drag-and-drop is the action of clicking on a virtual object and dragging it to a different location or onto another virtual object.
P.S.
It is taken from book “The Missing Manual“. I cannot tell that every page there opens new feature in Leopard for me. Certainly it is worth to read that book and to get information about features usage. I’ve started to regret, that I read 0 book about Windows XP usage at time what I was used it. Probably I would like XP much more.