Second Identity in Second Life?

How does the creation of a "new identity" in Second Life relate to your "real life" identity? What kind of experiments do we do with our avatars. Do we move the borders, if yes, does moving the borders in Second Life make it easier to transgress the same borders in Real Life?
In Second Life you don't have a body - it is not a physical universe. You can change and manipulate the avatar you rent at will and buy all the surroundings of your avatar. You rent your avatar, what in real world would be the core of your identity, and you own all the accessories, the clothes, the hair, the house etc. What role does the (real life) body play in the creation of an avatar and ultimately of an identity in Second Life?
The users talk of their avatars in different ways. Some talk of them as the virtual version of them, and insist it is them. Some insist the avat is another person, although with many communal traits, as if they have authored a personae. What is the difference between the two? They both give an edited version of themselves, as we also do when we present ourselves to our friends and family. Can we compare how the users talk of their avatars with how authors talk of the main character in a book they write?