The beta should start by the end of the year
If you have an interest in streaming your PC games to your TV, you can sign up to be in Steam's In-Home Streaming beta. All you have to do is join the Steam In-Home Streaming group, and Valve will pick some random people to test it out. According to the group description, the beta will start later this year.
Out of all the new Steam stuff happening in the near future, the streaming is the thing I am most interested in. My gaming PC is upstairs in my office, and it would be nice to play some games on my couch without lugging my tower down to the living room.