It's kind of nuts that Apple left the ability to share your music not just with other intranet users, but with the world. Share iTunes and Spymac already have set up lists of people with open iTunes running.
While you can't trade music via this method (not just yet), you can broadcast to anyone and listen to anyone else's streams via this feature. Apple just turned every iTunes 4 user into an internet radio station. If the RIAA or ASCAP or BMI ever catch wind of this, will they start asking every mac owner to cough up the 7/100ths of a cent for each user and each song played, according to their fee structure? Or is apple trying to nudge the net radio activist movement?
update: holy crap