When you read about a robot uprising (like the one in this week's review book, Robopocalypse), what you're usually really reading about is artificial intelligence taking over all the robots.
Most great horror revolves around the concept of losing humanity. Zombies are scary because they used to be human and they still mostly look human, but what essentially makes them human is gone. The same thing goes for vampires. And reanimated mummies, if that's your thing. Robots have the opposite thing going for them... they were not human, then we gave them what is the thing that makes us essentially human (however you define it: emotions, love, dreaming, etc.).
Another scary thing about robots is that we are responsible for them. Zombies are sometimes created by humanity (lab-created viruses are especially popular in the current literature) and anything arcane can be attributed to someone messing with magical objects or reading willy-nilly from spellbooks. But robots are 100% undoubtedly man-made, and so is artificial intelligence. We brought it on ourselves, so it was preventable, and that's part of why it's so terrifying.
It's scary for one other huge reason, too: they are meant to become smarter than us. With everything at a robot brain's disposal, it would be nigh impossible for them not to become smarter than humans. Their interconnectedness and enormous processing power allows them to think and experience and feel at a much greater rate than humans, making them superior to us in so many ways (combat, puzzle-solving, reflexes, and so on).
All I'm saying is, maybe you shouldn't beat the crap out of the printer when it jams. Someday it might hit back.