I got the Mary Poppins DVD a few weeks ago. Rachel's been watching it a lot and has gotten really good at some of the songs. She's just generally getting good at remembering tunes and words and singing, or even humming, along. So, the other day she was at my parents' place humming the tune of Supercalifragilisticexpialidocious. My father, who claims never to have seen the movie, recognized the tune and asked if that was what she was singing. She says it is and starts singing it, instead of humming:
Even though the sound of it is something quite atrocious
if you say it loud enough you always sound precocious
Evidently my father just about fell over from surprise. She sings it a lot now, and the sight (and sound) of a 39" tall three-year old singing "you always sound precocious" is hysterical. And, of course, she knows it's cute so she flirts while she's doing it...
The Straight Dope has an interesting write-up about the word (which I'm not going to type again).