There is a very valid reason why Valve has been silent when it comes to the implementation of twitch.tv broadcasting support for Steam and that is because they want everything to be self-confined within the Steam client itself. Introducing Steam Broadcasting, where you can now broadcast and watch others do so by merely using the Steam client itself.
This should be fun for people with a lot of close friends on Steam.
This feature is still in beta, thus it's still in its infancy. You can't add your webcam to the broadcast and the Steam client doesn't have a mic noise-cancelling, which is important for someone like me who listens to game sounds using my surround sound setup. The live streams are also not saved, which I am sure will discourage a lot of people from leaving twitch. But what's already here is indeed very impressive. All you have to do broadcast is set it up in the settings menu and the broadcasting starts automatically as soon someone is actually watching you, which is a rather clever and unique mechanism (not to mention groundbreaking because you're saving bandwidth if no one is really interested in watching) that can be set in a number of ways. To watch others, you only have to visit the Game Hub of a title you are interested in or by clicking the "Watch Game" drop down option in your Friends List. There is no option to follow someone's broadcast but I suppose you can always add that person as a friend. Perhaps Valve is more interested in fostering a more personal experience between the players and their viewers here than anything else but it is a little too early to tell where this feature will eventually lead us. Wherever it takes us, I am sure it will be an exciting place in video game broadcasting.
Since it's so easy to set up, everyone should definitely do it.