A friend of a friend I had a while back apparently wrote an appeal (more of a rant) to UCSF post-rejection and got accepted soon afterwards.
One of the associate deans there actually advised us that if we were really set on UCSF and felt that we could make a case for ourselves that we should address the letter to him personally.
I don't hear too many stories like this though.
Edit: I wrote this too quickly. Just to be clear, don't send in a rant. The girl in this case just strongly disagreed with the committees decision and was very passionate about the fact that she felt overlooked. It was probably a very good letter though.