If you're one of the people like me who use Steam on a big screen TV, then you'll be happy to hear that Valve is testing out a new design for the user interface. You can grab it now by opting into the beta for Steam.
After you do so, your Steam app will update and you'll be grabbing the latest beta version out there. I've opted into the beta a while ago and have never had any issues so if you want to be on the cutting edge of Steam updates, that's the way to go.
Along with updating the UI, Valve's also adding support for a multitude of audio formats such as FLAC, OGG, and M4A.
For you Mac folks out there, you're getting the initial run at being able to stream games, but currently only video works. You won't be able to hear anything or control anything.