Another question. Why, at the begining of GF3, did Connie introduce Vincent to Micheal at his office? They should be well acquainted.
It was more of an introduction for US (the audience).
Possibly SC, but it could also be more of a reaffirmation of who he was. Remember, Connie is Vincent's biggest supporter in the family, and by calling him "Sonny's boy" in front of Michael and Zasa, I think she is trying to give him some credibility.
Clearly Mike knows him because in the ensuing scene he tells Vincent that he had offered him a job in the ligitimate workd, and that he refused it. He goes on to say that Zsa took him in out of the kindness of his heart, and that whatever was going on between them was none of Michael's business. Before he washes his hands of it, however Michael does a clever thing. After Vincent says that Zasa is saying "Fuck Michael Corleone" behind his back, Michael (who clearly believes Vincent) gets Zasa to say that any man who would say such a thing was not a man, but "a dog."
After Zasa leaves, bloody ear and all, Vincent calls Michael "Uncle Mike," showing even greater familirity, and he tells Michael that he needs to be afraid of Zasa because Zasa knows that Mike is keeing him from rising in the commission.