I guess this is known for most of you, but still...
Dropping a file on a icon (ex. Applications) in the toolbar would result in that file being moved to the applications folder.
For me who always dragged between different finder win's
this turned out to be real handy.
This is an often overlooked things. I used to love the shelf on NeXT and for a while lamented it's passing in OS X Finder, but of course, you can drag folders to the toolbar, navigate someplace else, then drag items on to that same folder on the toolbar. Finally, you drag the folder off the toolbar when you're done.
This is a sort of drag-drop version of Windows' copy/paste for files.
Also useful is putting your favourite apps on the toolbar for quicker opening of files in a specific program. Usually saves having to clutter up the Dock and dragging much further