Mac OS X Lion (10.7) Introduces Cut & Paste Functionality

Command+C Selects files for copy or Move
Command+V Copies original file to the new location, leaves original file in original location
Command+Option+V Moves original file from original location to the new location. Original location does not contain that file anymore

Of course, you can still use the mouse to drag (which moves) files or Option+drag to copy files.