Streaming has become a huge business in the gaming world (with the likes of Twitch.tv at the forefront). Is there any possibility for someone else to enter the ring? Apparently, so long as you're Valve (Half-Life, Team Fortress, Steam). And today they announced a beta for Steam Broadcasting.
Steam Broadcasting allows you to tune into a friend's gameplay live, or invite a friend to watch your current session. Both players must opt into the Steam beta client first before being being allowed these options. Of course, just anyone won't be able to creep your stream if you don't want them to. Privacy settings range from allowing any Steam member to watch to only allowing specifically-invited friends.
Unlike traditional streaming, both users must be within Steam (in the client or signed in via browser) to spectate. Also, if no one is watching you play then you will stop "broadcasting." Only once someone tunes in will you begin streaming again.