I've had a Moscow Mule at the Bouchon in Yountville...If it's the same one, it's the best I've ever had! Of course, it helped that it was over 100 degrees and I was sitting outside--is there a more refreshing drink to have in the middle of summer? :)
I am a fan of the version at the Westside Tavern -- fresh ginger and soda in place of a premade ginger beer. Served in a glass. Find it much better than Bouchon's, the only advantage of which is the traditional copper mug.