Yes, at the tender age of 6 I believe, I saw an episode of the Ghostbuster's cartoon where it was revealed. The ghost of a Citizen Kane/Orson Welles character was finally reunited with Rosebud in the afterlife. Quite a charming addition to the story, however morbid.
I'll admit it was cute seeing a fat Citizen Kane going "WWWWEEEEEEE!!!!" on his dearly beloved sled once again.
No, I just saw it for the first time on the weekend, and my only spoilers (that I could remember) were from the Simpsons and that great Mr Burns episode. I didn't figure it out until about a minute before it's given away.