I understand WHY you should not do this, but quite frankly there is theory and there is practice. And in an era of long obtuse passwords I am thankful!
It's better when you work internationally. Our standard desktop admin password contains an @ sign. Which in most counties is shift-', but in the u.s. it's shift-2. It's not obvious which keyboard layout is in place (you also have to type user@domain, rather than domain\user, as \ doesn't exist as any key on the physical keyboard-mapping we have)
Password theory tells me that
Is an awesome password. 9 characters, capital, lower case, numbers and symbols.
It also tells me that
is rubbish, (or to be exact, "really good, if you put in a random symbol numbers and capitalise some letters")