The idea is to categorize music by the rhythm type, instruments, tone, tempo, key, etc. I tend to prefer music with a certain rhythm or certain tones (ex. subcategories of dance, hip-hop, soul, oldies, etc.). So, program a computer to categorize music according to these criteria, and assign a weight,
either positive or negative, to each classification.
The computer can play a custom mix of your preferred music, possibly pulling it from a P2P program or a commercial service (ex. Launch, Pressplay). It can also make the music more or less variable, and recognize patterns based on what music the user fully plays and when the user simply presses the next song button.
Naturally, it is also possible to categorize songs manually, either by the user or by some commercial service, but computer-classified music with user override is preferrable.