I think that the results are mixed at this point. Sarkozy, as president, has shown a willingness to "combine" his position as chief executive of France with that of the Union as a whole (for the temporary period he has in that role) to try and push creative diplomacy. But the lesson both from his efforts to broker a cease-fire to the Russia-Georgia conflict and from what happened in Beijing is that the effective of the EU rests to some extent on its ability to find a cooperative partner. Moscow and Beijing only went so far along in what they were prepared to do.
So the test is whether or not next month in Washington the EU emerges as the "broker" at the G-20. And the longer question is what happens when the EU presidency rotates, meaning that Sarkozy is no longer dual-hatted--what impact then?