I have a facebook account under my real name, and use it quite a bit to keep in contact with my family and friends. I have shut down my account a few times due to frustration with the GUI changing frequently, and concerns over the privacy settings, but I keep re-activating my account.
Twitter I really don't see a use for personally. I have considered signing up, just to follow a few choice people, but in the end you don't really need to sign up to do that.