The thing is, Sarkozy is not campaigning for the US. He will put France’s interest first, and that is why he was elected by French citizens, just as the US President isn’t elected by US voters to cater to France’s needs or desires.
You can trust Sarkozy to strongly support the United States when it does mean France will be stronger as a result, whether morally, economically, or politically. But expect him also to say “I disagree” on some issues.
I actually see no problem in friends disagreeing with each other now and then. Areas that we will see the disagreement, IMO, are Kyoto (unless the US elected a democrat president), and Iraq war. Many Americans were angry because Chiraq went further than simply disagreed with Bush. He actively sabotaged whatever attempts Bush did to get approval from the UN SC. Still, none of those are latent. After all, the US now has close relationships with Japan and Viet Nam, two former enemies.