@flip - it is free and works with PCs, Macs and Linux. Just install the desktop version from
www.simplifymedia.com and then the iPhone/iPod Touch version via Installer, and you will have access your entire music collection wherever you have WiFi. Music is streamed computer-to-computer within your set of machines and also with friends (limit 30). All streams are encrypted for privacy.
Two additional notes about the iPhone/iPod Touch version:
1) the connection to your iPhone/iPod Touch is one-way. it plays remote music but does not serve
2) we haven't added proper navigation for the "all songs" category (but iPod-like browsing by artist, album and genre is coming very soon). So, it really helps if you have already set up playlists.
On the plus side, unlike mobile safari based solutions, you can keep surfing the web while you enjoy remote music.