Using the Option key to switch the default behaviour of tab works in most applications with a find box (Safari, TextEdit, Terminal, etc), and even works in some applications with multiple text fields. For example, Option-Tab in Eudora allows you to tab from the body field to the subject field instead of typing a tab.
One disappointing exception is Mail. The only way to escape the body of the message from the keyboard is to Shift-Tab (incidentally, there is also a bug in Mail that stops you from tabbing between the fields in the find/replace dialogue box ... again you have to Shift-Tab).

