You’re looking at a Finder window and want to view the Desktop level (because your Desktop’s a mess and it’s easier to view a list in the window than those icons scattered all over). Out of long-ingrained habit, you press Command-D to look at the Desktop-and find you’ve triggered the Duplicate command, coping whatever was selected in your window (your entire hard drive?).
Change the Duplicate shortcut from Command-D to something you won’t hit by accident:
1. Open System Preferences > Keyboard & Mouse and click the Keyboard Shortcuts tab.
2. Scroll to the bottom of the list and select Application Keyboard Shortcut.
3. Click the Add button beneath the list.
In the dialog that slides out:
4. From Application, choose Finder.
5. In Menu Title, type Duplicate. (Never mind that it’s not the menu title!)
6. Click in the Keyboard Shortcut field and press Control-D.
7. Click Add.
This is excerpted from my ebook 33 Things to Customize in Leopard Right Now.