Charon121: Humans already became cyborgs when they first started using simple crutches, clothes, hairpins, glasses and hand-held tools. All those are examples of technology that extends the abilities of the human body or enable it to perform functions it was not been given by nature. Cybernetic limbs, hearts, brains and other organs are the same thing, only a bit more refined. In order for us to be fully "human", we would have to revert to animal ways and do only the things that we can accomplish using our teeth and nails, protecting ourselves with nothing but our skin.
That is not what cyborg means, for one they have to be built into the human body. Glasses just correct your site, if you replaced your eyes or your retina maybe but glasses don't make you a cyborg. Secondly the beyond human limitation is not about fixing problems so you work as normal, you would have to work beyond normal. So a pacemaker only corrects the heart to normal if it allowed the heart to beat beyond normal endurance then that would potentially be in the realm of cyborg.
Your last statement is interesting because there are many animals that use tools and intelligence(birds and Apes come to mind) so why are they natural - or are you saying they aren't?