As I have very poor keyboard and writing skills I will discuss this in several parts, but I have done extensive studying of this character to the point of watching the entire series over 10 times start to the last ep, took notes, and did many web searches including reading interviews with Summer Glau. I think I have come to conclusions that nobody else has ever considered to my knowledge (based on information presented thus far in the series and disclosed events of upcoming episodes) The points I will make and go into in greater detail and the reasons I believe them to be true will be, but not necessarily in this order, the following...
1. In the future John and Cam have a very close personal relationship. I know that a lot of others have also come to this conclusion as well but there are some things I'd like to point out on this. I will state here and now, however, that while I don't rule it out 100%, I don't believe it to be of a sexual nature, but more like a close brother sister type thing.
2. She was originally built by Skynet to assinate John, ended up totally loyal to him....but, she was never actually "reprogrammed"
3. While she is in fact technically a "machine", Cyborg, Android or whatever, she is in reality 100% human (with a few very minor exceptions) and must be looked at in this light to fully understand her actions.
4. She was (in the future world) a "secret agent", spy, espionage operative or whatever working for john.
5. She is, will be or was (the element of time travel makes things a bit confusing at times) a very, very important key figure in the ultimate victory of the humans over Skynet, perhaps even on a level of John himself.
6. Derick will ultimately come to fully trust and consider her a "brother/sister in arms".
All of these points are dependent on the show continuing of course..which I hope it does.