Neat topic. I like it.
The Good:

HC "Barney" Barnum - Medal of Honor recipient. I only sent a LOR and 2 index cards. He returned 1 signed, and sent a huge envelope full of information about the Medal of Honor, his actions in Vietnam which earned him the Medal, newspaper clippings (photocopies of) and three pictures.
No, I am not giving out his address.

Paul Wiedorfer - Medal of Honor recipient. I sent a letter and 2 index cards. He sent back both index cards signed, a copy of what he did during World War II which earned him the Medal, and a small medallion that has his name, Medal of Honor insignia, and the date he performed his actions. It made me cry.
No, I am not giving out his address.

- Jimmy Smits - I wrote a letter to him, included a picture of him in Cane and my Anna in the Tropics (a play) he was in in Princeton, NJ. He signed the photo and the ticket, and wrote a lovely note back about performing in Princeton and how much fun it was.

LuAnne McLane - I wrote her an email ages ago, and she emailed back. We continued to talk like that for a while, when I asked for an address to send a SASE to so I could get her autograph. She told me and sent me a signed authors proof copy of her new book, signed and dedicated.
The Bad:

Placido Domingo - sent multiple letters from the mid 1980's to 2004. Got at least 3 back as RTS, and others never answered. Then I did get two, but it was
at least 4 years, more likely
12-15 years waiting. The photos I'd enclosed were not used.

Alex Horley-Orlandelli - illustrator/artist - RTS - Refused.

Maggie Shayne - author - RTS - Refused
I'm sure there's more