Okay okay, we make the Skynet and/or Hal 9000 jokes often enough (and personally, I make reference to Michael Critchton's book, Prey), but in all seriousness...it really isn't gonna happen. Why? Well, I have some reasons right here.
{1} We are as far away from a proper AI as we were back when Robbie the robot made his debut in the movies. A real and actual truly independent thinking machine does not exist yet and we still don't know how to make one. With apologies to Kevin Flynn and the makers of Reboot, this shit ain't easy. The most complex thinking program thus far is still a heavily-programmed if-then statement machine. No more, no less. Until your turing test comes back unexpectedly with the phrase "Fuck this, I'm going to Vegas.", you have no AI.
{2} At this point, with the sci-fi jokes being made all the time, I highly-doubt that anyone is dumb enough to put a thinking machine in the position to properly annihilate us. Even the relatively-benign style of Wargames is a cautionary tale towards being overrun by machine over man. Put simply, that line of thinking will forever keep the AI as the underdog of society, which is ironically something Isaac Asimov certainly hit upon when he used his robot novels to deconstruct classism and prejudice. If anything, they'll get passive, uncontrolling roles if they DO come.
{3} If all else fails and we actually come face to face with AI-driven monsters and mechanized armies trying to lay waste to humanity, there is this one final thing that will most-assuredly ensure our safety, and that is human imperfection. Not because humans are imperfect, per se, but because our creations will ALSO be flawed. The X1A-MegaBrain goes homicidal and decides to kill humanity! It clears all nuclear launch codes, prepares for launch, and...promptly blue-screens because of a missing or corrupt applet. The greatest computer geniuses can't or won't prevent software foul-ups. What makes you think this will be any different once the AI goes loose? The Death Army and the Devil Gundam collapse in mid-stride, thanks to incomplete programming.