If you're reading this blog, then you might like recommendation engines.
I've been continuously impressed by Amazon's recommendation engine. As I've expanded what I buy through Amazon (heart rate watches, cooking utilities, computer peripherals, etc.), Amazon has done a very good job of processing those likes -across categories- and making very intelligent suggestions that have resulted in purchases.
Apple, on the other hand, can't seem to figure out what MUSIC I like despite having bought numerous albums and even being signed up for their artist alerts… Apple constantly alerts me to new hip hop and r&b content. I bought some snoop dogg two years ago…but I'm no big hip hop fan. What about Dave Matthews? I've probably bought about 5 albums. Alerts about Dave? Zero.
I'm aware of the "gift drift" that you can get with Amazon if you buy a friend's kid a copy of The Gruffalo- for the next several months you get offered children's books non-stop (I've actually never had a problem with Amazon's recommendation engine).
Looking forward to the mobile internet, recommendation engines- or agents- are going to become even more relevant- who's around you, what they are listening to, and why you might like it, that your favorite store (based on transaction history) has your favorite stuff on sale and the bus is 12 minutes away… etc.
Apple is smart (understatement), but the problems they have with recommending good music underscores the challenges facing recommendation engines.
If this is something that you're particularly interested in, O'Reilly has published a great book on the topic:Programming Collective Intelligence.
Highly recommended reading.