As usual, Charles Krauthammer says it better than I can. Here's his take on the speeches by President Obama and President Sarkozy at the Security Council, as well as U.S. policy toward Iran.
In the coming weeks and months, I think we can expect a dribble of news in the pattern that's just been set: the United States or the International Atomic Energy Agency will be forced to reveal some intelligence proving that Iran is working as hard as it can to get nuclear weapons. Iran will refuse to discuss anything of significance, offering instead meaningless 'concessions' that buy it some more time. And Obama will claim victory for his diplomacy and personal charisma.
Then, when Iran has the bomb, we'll urge Israel to dismantle its nuclear weapons so that the Mideast can pursue disarmament. If Israel attacks Iran to try to stop or at least damage its nuclear program, we'll apply sanctions - to Israel.