If you are familiar with the old OS X way of modifier keys with dragging, you will know that holding down the Command key will force an item to be moved (as opposed to copied).
In Panther, if you are an administrator dealing with a root-owned file that you have no write access to, you can move around and trash the file by holding down the Command key as you drag.
This is a most excellent and useful trick that will save many a trip to the Terminal!
[robg adds: In testing this, it became very obvious that the purpose of the Command key has changed in the Finder. No longer can you Command-drag to move something; in fact, on two machines, I couldn't use Command-drag at all -- holding Command and attempting to click on something fails. Instead, click and hold the mouse button first to drag the item, then press Command and drag the item around. This is a very useful trick - when dealing with root-owned files, you'll notice that the "can't write" symbol (the slashed circle) disappears as soon as you press the Command key while dragging.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20031025000815163