Adding the "show the desktop" icon back to the "quick launch toolbar" is easy under Windows, just do this:
To re-create the Show desktop icon yourself, follow these steps:
1. Click Start, click Run, type notepad in the Open box, and then click OK.
2. Carefully copy and then paste the following text into the Notepad window:
[Shell]
Command=2
IconFile=explorer.exe,3
[Taskbar]
Command=ToggleDesktop
3. On the File menu, click Save As, and then save the file to your desktop as "Show desktop.scf". The Show desktop icon is created on your desktop.
4. Click and then drag the Show desktop icon to your Quick Launch toolbar.
Under Linux, you right click on the tool bar and select add new items
I think pulling up notepad and creating an ini file is the best method though. Cuts out the folks that really don't need that icon!