Half the world (the half that is underage at least) seems to have gone crazy for High School Musical.
But it cannot be the plots (largely lifted from Shakespeare) or the acting (no great shakes) which have made it so popular. The clue of course is in the "musical" part. It's the High School Musical songs which have everyone following it.
These are what Disney are good at of course and the songs are indeed good enough that many of them have gone on to climb the Billbaord charts, as have the sound tracks.
If youre interested, click through that link to see a full listing of all of the songs plus who sang them and why.
For it is indeed the songs and the music that make High School Musical so popular.