cmd-option-shift-delete has been around since at least since OS8 (1998). I don't know if it was in System 7; anyone know?
In Finder,cmd-delete = move selected item to trashcmd-shift-delete = empty trash (with warning prompt; locked files not deleted) cmd-option-shift-delete = empties trash without dialog, included locked files
When emptying the trash of hundreds of files including some locked files, the "Empty Trash" process will be repeatedly interrupted by the "stop or continue" dialog box each time a locked file is being processed. This dialog box demands a mouse click response before continuing with the emptying of trash. The cmd-option-shift-delete avoids this entirely.
In Tiger at least, you cannot drag or send a locked file to trash - you get the same "operation cannot be completed" dialog. However, you can lock a file while it is in the Trash. To get rid of it subsequently, it means unlocking the file or using cmd-option-shift-delete.
Sometimes, some files persist for some strange reason. In which case I grab a 3rd party software from the net, e.g.:
During startup, cmd-option-shift-delete will bypass the startup drive and boot from the next available disk with a valid OS ( e.g. a second hardisk or an external or CD).
Inherent and 3rd party keyboard shortcuts are a must for power users who hardly need to touch their mouse. I remember thinking I was good in '99 until I saw Gregory Chan on my Powerbok 1400cs keyboard - boy was he was fast! It requires practise but the speed bump is usually worth it. Programmes like Microsoft Word allow customisation of keyboard shortcuts for almost all of their functions and formatting. If you are a frequent user, it makes a significance difference to use this.
I lost all my Word 5.1/98 customisation when I stopped using Word - only had to pen and share short documents so used Text Editor/Text Wrangler instead. I am beginning to have to use Word again, so I am going to have to re-learn some of this.
Keyboard shortcuts aren't for everyone though, some people love to crawl along with their mouse.
For Finder shortcuts updated for Leopard, see: "Mac OS X Leopard: 200+ Productivity Booster Keyboard Shortcuts." Usingmac.com, 21 Nov 2007.