My two favourite memories of Walt Disney World are the following:
Last Christmas day, we started our tour of the Magic Kingdom at the Toontown Hall-of-Fame. Naturally, there were no other guests there that early in the morning, so Cinderella just picked up my then two-year old daughter, and gave her a roughly 10-minute personalized tour of all the character rooms there. Our daughter was, of course, thrilled, and we got some great pictures and memories!
My second favorite occured just a few weeks ago when my now three-year old daughter rode Splash Mountain for the first time. My wife decided to stop by Guest Relation to see if they didn't have anything special for such an occasion (which I at first considered a waste of time), but sure enough, after 10 minutes the Guest Relations CM she talked to returned with a wonderful, personalized "Magical Moment" certificate, awarded to her from Mickey Mouse ("Congratulations on your first time on Splash Mountain. Your Pal, Mickey Mouse"). It also has signatures of Minnie, Goofy, Donald and Pluto on it. It is now in a frame mounted above her bed.