I'm watching my friend's dog while they are out of town. He has separation anxiety so he is a nervous dog. I take him to work with me and he stays with me in my office. If I leave my office for a few minutes, he is so excited that I came back that he jumps on me. Ordinarily, this would not bother me, but this dog is a little over 100 pounds.
My friend agreed that the jumping is a problem. In talking to her about it she said that there are times when they invite him to jump up on their shoulders. (Light bulb!!)
This dog has learned that it OK to jump on people because he is sometimes allowed to do so. Dogs need consistent training in order to avoid unwanted behaviors. This dog should never be permitted to jump on anyone because he is unable to distinguish when it is OK and when it in not OK.
If you have a behavior that you do not want repeated, you need to have the same response every time. In that way the dog can learn what is expected from him.
So the moral of this story is, if you get a cute puppy that is going to grow to 100 pounds, don't ever let him jump on you unless you are willing to accept the consequences.