In the United States it is nearly a cultural universal--everyone knows what it is. MOST people know that it isn't a real word. EVERYONE knows that it is from the movie, "Mary Poppins." It's used playfully. If you happen to use it in a group of people, there's a pretty good chance that someone will start singing the song. It isn't a real word yet--it's part of the Mary Poppins world, just as "muggle" belongs to the Harry Potter world. When people say the word, 90% of the time they get a quick mental picture of Julie Andrews in the movie. It is first mentioned at about 0:33. https://www.youtube.com/watch?v=1Pu1adxqUAg English being what it is, if people simply keep using the word "supercalifragilisticexpialidocious" for another decade or so, and people keep using it without knowing that it's from Mary Poppins, it could well become a dictionary word.

I agree with Phil, it's really a nonsense word. And, surprisingly, (or not) it has made the dictionary. It's popular culture, so many people are familiar with it, but I can't imagine it being used, except jokingly, among friends. Also, let me correct you, the word is - "supercalifragilisticexpialidocious". Have a look at the Wikipedia article: http://en.wikipedia.org/wiki/Supercalifragilisticexpialidocious

It's a word from Mary Poppins that was invented specifically to be long for humour. Everyone understands the reference, but it's not an actual word with a meaning.

It's from Mary Poppins. It's probably in the dictionary by now, but I wouldn't consider it a real word.

I use it a lot actually e.g. please pass me another one of those supercalifragilisticexpialidocious biscuits - they are very yummy. However, it may be just a regional variation (i.e. just in my house!)