How Secure Are Memories?

Here is a link to the video from class where Derren Brown convinces Simon Pegg that he's always wanted a red BMX bike (with an explanation afterwards!).

This clip seems to indicate a problem with relying too heavily on memories to serve as a criterion of personal identity.  If our memories can be changed, then how can I say that I am my memory?

This video also raises some questions about moral responsibility.  If we can be controlled by other people, are we responsible for our actions?

Here is the link to Derren Brown's The Experiments: The Assassin.  In this video, you see Derren Brown attempt to brainwash and hypnotize someone into being a sleeper assassin.

In another video, Derren Brown's The Experiments: Guilt Trip, Derren tries to convince an innocent man that he is guilty of a murder that never happened.  This video raises concerns about the reliability of memory and questions about moral responsibility and its relationship to feelings of guilt.