Today Mojang released Minecraft Snapshot 13w47c. This snapshot is for Minecraft 1.7.3, and it adds only one new feature into the game: Twitch.tv intergration. Once you visit your Mojang account settings on Mojang's website and link your Mojang account with your Twitch.tv account, you can begin broadcasting in-game just from the simple click of F6. Players can alter their quality, framerate, bandwidth, microphone volume, system volume and compression settings via an in-game options menu called "Broadcast Options" under options. Players can also change which key begins/ends the broadcast by going to the key binding settings. As of right now, this feature is only available for Windows XP and higher and for Mac Lion 10.7 and higher. Will you use this feature? Let us know in the comments!
Source: Mojang, Minecraft Wiki