Well even if you don't and you have them (it?) carefully memorised it seems that a five character lowercase password could be cracked in 11.9 seconds using a brute force attack. This piece over at lifehacker goes on to show that mixing up that password and including upper case characters and special characters ($%^& etc.) increases the time it will take to crack your password to 2.15 hours. Go up to eight characters and include some from the possible set of all characters and it would take 2.1 centuries with the current state of the art computer systems and code.
Eight characters is not so hard to remember. Is it?
Article first seen linked at Daring Fireball