In Snow Leopard, if you right-click on Trash icon in the Dock (or left-click and hold on the Icon), you'll get a menu that allows you to empty the trash. If you hold down the Command key while this menu is being shown, the option to empty the trash will toggle to become a secure empty of the trash. If you let up the Command key, it goes back to the regular trash emptying. This is a great shortcut if you have something in the trash that you want to empty securely.