The remark is interesting because a prominent European leader said out loud what everyone believed but did not dare say: the missile shield is useless (in its current conception) and the Europeans don't really want it. The reason why he probably chose to announce this now is shrewd and shows he can see which way the wind is blowing. While it was obvious that Bush would not take the hint that the project was useless and a remark would have only highlighted the powerlessness of whoever said it; Sarkozy is betting that Obama will eventually back off on this project and he is probably right in that regard. The logic that the missile defense is not aimed at Russia but at some "rogue" state, while being deployed around Russia, did not convince anyone; it is mostly seen as a response to Russia's "aggressive" behavior. A back off on this project is probably the first thing that an Obama administration will be ready to give when they talk with Russian leaders, because it is more of a symbolic move than anything, given its overall uselessness, and Obama has stated during the campaign that he plans to cut investment for "unproven" missile defense systems so he could convincingly sell this move on the domestic front as something he had planned all along.
In the end, Russia will remember Sarkozy as the first one who spoke out against the missile defense system and domestic opinion will remember that he, contrary to Blair, could influence American Presidents. That is probably what he's banking on. Shrewd move.
Hat tip: Cernig at Newshoggers