1. She is the quintessential mouthpiece for the Bush administration. We may cite this as a flaw, a sign that she is merely a puppet, but from a diplomatic perspective, I can imagine that it would be easier to deal with a Secretary of State who one knew was speaking directly for the President. There would be no ambiguity or mixed messages.
More below the fold. Feel free to add on.
2. The line of influence is one way only. She will be the mouthpiece for Bush/Cheney but she will not have their ear. Powell at least was able to persuade Bush to go to the UN Security Council. I doubt that Rice will have anything like that kind of sway. But, this also means that she is not going to be making policy, which at this stage seems a good thing.
3. To put it in crude terms, Rice has made it absolutely clear that she does not give a shit about diplomacy. Her real aim is the Pentagon: specifically, she wants Rumsfeld's job, but she is not going to get it until Rumsfeld has had a chance to rehabilitate and redeem himself. I give him two years. It is likely the case that Rice cut a deal with Bush that will allow her to move over to the DD at the mid-term point, which means that her already minimal investment in diplomacy will be all the more limited for having a time limit set in advance.
4. Better her than Wolfowitz.
5. Jack Straw does not have anything like a close working relationship with her, certainly not the kind of relationship he has with Powell. The Bush/Blair team will forge on, but I think there will be some kinks in the foreign secretary relationship.