The Slate Star Codex (a blog with a strong rationalist bend) has written a couple of rather interesting musings on the issue of AI:s.
Well worth reading. It's also a rare blog in that the commentary section is often very much worth reading.
A collection of arguments on the risk of AI:s pose.
On the issue of why we should be studying AI now rather than later.
On the question of what could an AI do without a body.