iLeech is a Mac OS X application that will connect to an iTunes 4.0.
This is accomplished locally using Rendezvous/zeroconf/mdns/whatever, or if you know the IP address of a machine you can access it's playlist via daap:// (provided port 3689 is open). However, you can only stream the music from the iTunes host -- no copies are made on your machine.
iLeech will connect to an iTunes host, display their playlist, and allow you to copy the files to your local drive. It can be downloaded by clicking the "Download" button from the navigation bar.
And all I can say is "Wow". In my wildest dreams I would not have imagined the reaction/attention my simple little Java/Cocoa application would receive. When I initially released it, I had honestly never imagined more than a couple of dozen people would be interested in it. Call me naive if you will, but that is the truth on my end. But that idea has certainly been shattered during the past week, as in the first 4 days the page received an overwhelming 9,399 page views (and 2,147 downloads)