Well, okay maybe not as a fantastical idea as one might think. (No, we aren't going to all become like members of the Avengers... at least no time soon.)
A month ago, we learned how to survive a robot uprising. Today, we learn about how a future where we create new technology that makes us effectively into "super-humans," and how this will likely affect our social setup:
A lot of this is developed in near-future sci-fi, as well as role-playing games like Shadowrun. I used to love the idea of the Street Samurai, with all its cybernetic implants. The balancing of these - for gaming mechanics - was that the increased number of implants was a trade-off in magic and humanity skills (and often weight and bulk).
In other novels, in which cyborgs had become an increasing part of the social landscape, "trading in" a leg (or even upgrading your legs) was done by some for both aesthetic as well as functional (or increased-functional) purposes. See, for example, the Transmetropolitan graphic novel series (which deals with a somewhat-in-the-future, but not intergalactic space, setting) and the Battle Angel Alita and Battle Angel Alita Last Ordergraphic novel series (which are set in a dystopian future of a collapsed solar-system-wide civilization).
What I find interesting is how cyborg enhancements play such a small role in the Star Trek series, save for the calmly, callously, inhumanly, evil Borg...