It's a bit gross, but that's not my main reason for not letting our dogs lick our dishes. Dogs who do this often become over weight and they become beggars which I do find extremely annoying. If I'm eating at someone's house, I do not like a dog with his head in my lap or sitting next to me with begging eyes.
Our dogs only eat dog food -- not people food. That's always been our rule with pets and it really stops the begging. When our dogs see us setting food on the table, they automatically go in their crates because they know it's dinner time and the food isn't for them. If they see us with food, they pretty much stay away. Now, if someone sets a food item down and walks away for a moment, it's fair game.