Here's my entry.
The actual problem with cybernetic implants, once they reach the consumer market, will not be the question of how much humanity is left. That will be discussed, of course, but it'll probably only get some real relevance once we begin tampering with our brains, which might take quite a while longer than simply replacing a limb. A man losing a leg and henceforth wearing a prosthetic one doesn't make him cease being human, after all.
No, the actual divide will be social. The divide between "advanced humans" and "naturals". You don't have to play Deus Ex to see that. And I can't imagine prothetics that are so good that you'd be willing to replace healthy limbs with them will come at prices being affordable by everyone. Just imagine the job market in such a scenario.
On tattoos... Well, they are not an option for me. For one, I have too many melanomes in the way, which if disturbed by needles may well turn cancerous. But, being a social phobiac, I'd be too shy to get one, anyway, even though noone would get to see it, which in turn would make it pointless to boot.
In closing, to everyone interested in the topic of transhumanism, of which cybernetics are a part, I'd also like to recommend the Transmetropolitan comics (DC). Quite the radical view on possible consequences of certain technologies. For example, reanimated people that had their heads cryogenically frozen at some earlier point in time, waking up, disoriented, shocked by how much the real future deviates from their earlier chrome-plated imagination, housed in asylums, where they eke out the rest of their sorry existence. Or take this gem (only communicated via a poster ad in a single panel of a street view): We can clone human body parts now? Then why not do away with the taboo on cannibalism?