Cyborgs are one of the more common variations on the human condition that you see in science fiction. They are typically found in situations where the integration of man and machine has been taken to what some see as a logical "next step" along the technological advancement timeline. This can mean a robotic hand (Luke Skywalker in Return of the Jedi) or any other sort of technological integration up to, and including, an almost wholesale replacement of organic pieces with mechanical pieces (the Borg of Star Trek fame).
If you read any significant amount of science fiction, you've seen cyborgs at least once. Whether they're good, bad, or indifferent, there are enough stories that you're bound to run into them.
This picture of Lincoln is the kind of thing you can expect to see with steampunk cyborgs. Gun arms with multi-barreled machine guns, a few metal plates here and there, and maybe some steam-powered accouterments such as mechanical legs or even mechanical innards. One of the best examples I can think of is Whitechapel Gods by S.M. Peters. It's more clockpunk than steampunk, but the theories Peters presents in creating the gold cloaks and black cloaks are sound examples of cyborgs in steampunk.
Now, the science-knowledgeable among us might dispute the possibility of people integrating so fully with machines. And they're right to do so. The current level of technology we're at doesn't allow for the wholesale integration that the creation of a cyborg would require. Look at the movie Robocop. There's no way the technology of the 1980s could've possibly created someone like the titular character. Robotics at that time could, and still can, barely manage to make robots do what is required of them without constant commands. That said, recent news reports and advancements in the science of cybernetics are bringing cyborgs closer and closer to reality.
But what, you may ask, does this mean for the writer of steampunk?
Well the burden of proof is both higher and lower for a steampunk writer. Higher because you're potentially working with less-advanced science (although the Ancient Greeks had robots), but lower because people accept that certain advances need to be made before cyborgs (bionics in CALLARION AT NIGHT) could be created. You need merely say that person X made these discoveries in order to ensure that the reader isn't drawn from the story.
This is, of course, the opinion of only one humble writer. But I am curious about one thing. With the ubiquitous nature of cyborgs in science fiction, is there anything you can think of that would make you not believe in the possibility?
P.S. Don't forget about the Ten-Word Novel Contest! The deadline is December 31, and the winner gets the lovely New Year's gift of a book of their choice. Ten people have already entered, so the competition is growing.