I am relieved to see Hillary Clinton as Secretary of State, for the same reasons I would have been happier to see her as Commander in Chief. The lady is tough, and is probably perceived as such by those who have little reason to assume the same of our President-Elect.
As my husband, the Hoosier Gadfly, said in an email to a friend: "[H]aving a gimlet-eyed sociopath to intimidate one's adversaries is a big asset. She really is something out of a Nietzchean nightmare - the abyss that gazes back at you." He is looking forward to seeing her effect on Putin.
I also suspect that Obama wants her handy for good cop/bad cop routines. "Respond favorably to my warm smile, or the next meeting will be with Medusa here...."