For those of you looking for something a little different for the Mozart Year, there's always this interview with Glenn Gould, where he gives some of his infamous thoughts on Mozart ("a composer who developed towards mediocrity").
There's also the great line from the movie Vertigo, where James Stewart is in a sanitarium, and Mozart music is being pumped into his room as "musical therapy." Barbara Bel Geddes ends the scene by telling a doctor:
"You know what, doctor? I don't think Mozart's going to help at all."
And finally, there's the comments of Beethoven on Mozart's operas:
"I could not compose operas like 'Don Giovanni' and 'Figaro;' toward them I feel too great a repugnance. I could never have chosen such subjects; they are too frivolous."
Take that, Wolfgang!