A part of the iOS 4.3 update, iTunes Home Sharing lets you stream media from a copy of iTunes on your network to your iPad, rather than having to first transfer it during a sync operation. In addition, Home Sharing helps keep your library up to date. When you purchase a song on an iOS device and then connect to your iTunes library wirelessly, the song is automatically transferred to your library. It’s like turning your iOS device into an Apple TV.
(Via Shawn Blanc.)