Have you ever written fan mail to a celebrity? Did they respond and do you have any tips on getting the letter to the intended recipient?

There are so many actors, writers, comedians, musicians and artists I'd like to contact just to let them know how much I appreciate what they do. With the recent loss of Robin Williams I realise there is a limited amount of time that this is possible... I am curious to know what your experiences have been in connecting with these inspiring people and any tips you might have in contacting them.