Glados saying goodbye to her daughter. aka: Chell if you believe all the speculation.
Okay Caroline IS NOT Glados and Chell is not Glados daughter, although she may or may not be Caroline's daughter. Caroline is a ghost in the shell.
Ill explain, during one of the past Aperture science facility levels, Cave Johnson talks about AI and digitising people's personalities. So let's say that at some point after Cave's death Caroline had this done and she was stored digitally. Now the place starts to decay things start to go wrong and you start to get some cross system corruption. Caroline starts to spread, starts to crop up in a whole host of facilities computer AI systems.
She gains some access to Glados but Gladoses desire to research and do science and the level of power she has over the facility clouds the Caroline effect. We see this when Wheatley takes over from Glados, he goes from being quite nice and jovial to a power mad idiot, in this place power really does corrupt. On the flip side Spud Glados has more chance to be effected by Caroline given that she is no longer being driven by research and science and the power of controlling Aperture.
So what about the turrets, well Glados doesn't actually control the turrets, if she did why would they have the personality loading and testing line you see whilst digging round in the bowels of Aperture? Chances are this 'Caroline effect' has managed to get in to the turret production line at some point along the line, remember you save a turret that claims to be Caroline and then says 'I am different'. Like the defective turrets you see getting trashed some of these faulty Caroline infected turrets would have been caught and destroyed but many would have gotten away. This is further shown by an easter egg of one fat turret conducting a three turret opera in one of the early test chambers.
The final proof is Gladoses behaviour overall. If Caroline was core part of Galdos rather than just a suppressed rouge element of code then Gladoses behaviour is not that of mother to daughter and Glados actually says at the end that the events of saving Chell's life had taught here an even more valuable lesson 'where Caroline lives in my brain' she then deletes Caroline. Sounds like a rough bit of code to me.
That's my theory, Caroline is a ghost in the machine, a rough program that may or may not have resulted from the uploading and storage of the real Caroline's personality at some point Aperture's early history.
