Agree with Irish here.
Cotillard is definitely not a recognizable name to the average movie-goer yet.
I wouldn't be surprised if that changes in the near future, with her being in the new Batman film as well as a few other high profile roles.
I don't think she's there yet, though.
You could, I'm sure, remind people of her by saying "Leo's crazy wife in Inception" or something, but just reciting her name isn't going to get a huge response.