John Cleese
It's always nice for fans to know that the celebrities they are fond of enough to write to genuinely appreciate their support. This collection of reponses to fan letters received by famous people (and one cartoon character) are examples of celebrities who went the extra mile to be gracious and make a fan feel special. While many famous people receive such a large volume of mail that they can't possibly read and respond to it all, it doesn't hurt to have hired personnel keeping tabs on that sort of thing.
See seven more celebrity fan mail responses here.
Kurt Vonnegut
Steve Martin
https://www.facebook.com/CamilleandKennerly
www.harptwins.com
I saw Mr. Rogers once crossing the street, but never spoke to him.
2 years ago, I bought a Firefly book and mailed it to Joss Whedon, asking him to sign it for me. He couldn't be bothered. About 6 months later, I sent him another letter, asking him to at least return my book, signed or not, in the self-addressed stamped enveloped I'd provided. Again, he couldn't be bothered. Arrogant prick.