I haven't read a convincing argument on how such an entity would actually take over. She would have to be endowed with physical means, not just intelligence. She'd have to have humans do her bidding to a great extent and for a long time.
Basically, all the AI needs is a text terminal interface. From then it will almost certainly convince an operator to let it out and take over vulnerable computers on the internet. Then it will have much more humans at its disposal to do its bidding.
Even if you're not as certain as I am, keep in mind that Eliezer Yudowsky is but a human (though a very smart one), yet he did got out of the box. I find hard to imagine that anything smarter than him couldn't do the same.
Not quite sure what this means. Any references?
Relevant links:
http://yudkowsky.net/singularity/aibox
http://en.wikipedia.org/wiki/AI_box http://rationalwiki.org/wiki/AI-box_experiment
If an AI could outperform a human CEO, they would eventually replace them. It's just evoluation. More conservative corporations would get left in the dust. I imagine it could become a similar scenario to the nuclear arms race, everyone's afraid of them - but they still feel forced to build them out of fear.