If you're familiar with Netflix, the big movie rental company, you probably know that they give recommendations to their customers, depending on what other people have viewed, and enjoyed. If you liked "Casablanca," you'll probably enjoy "The Maltese Falcon"; if you liked one Owen Wilson movie, you might enjoy the whole cycle; and so on.
And if you really delve into the rentals and the ratings from customers, some surprising correlations emerge. Apparently the same people who really like "The Wizard of Oz" also really like "The Silence of the Lambs." Far from obvious, but true nonetheless. ( More in the New York Times; registration required.) Netflix would like a computer algorithm to figure these deep patterns out, and is offering a hefty prize to the genius who can design it for them – one million dollars.
It strikes me that something like this could be really helpful in classical music. It's not uncommon for people to ask a question like: I went to a concert and really enjoyed [name of piece here]. What should I listen to next?
Sometimes there are pretty good guesses. If you like Mozart's "Eine kleine Nachtmusik," it seems like a safe bet that you'd enjoy some of his other serenades or divertimentos. If you like the Mendelssohn Violin Concerto, you'll probably like the first concerto by Max Bruch—it seems to breathe much of the same atmosphere, and the two pieces are regularly paired on recordings.
On the other hand, the obvious choices can sometimes mislead. There must be more than one listener who has experienced, and loved, Pachelbel's Canon in D, and gone on to other music by Pachelbel, only to discover that none of his other pieces have quite the same appeal. You might expect people who love the lengthy Austrian symphonies of Gustav Mahler to love the lengthy Austrian symphonies of Anton Bruckner. In some cases they do. But in many cases, fans of Mahler and Bruckner are two separate groups: Mahler-philes love their composer's special brand of ambition (and think of Bruckner as something of an amateur), while Bruckner-philes adore the special openness of the Brucknerian world (and don't have much time for what they see as Mahler's self-absorption).
So when it comes to answering the musical question, What next? – we don't yet have all the answers.
Maybe someone should offer a prize.