The spectating client will allow viewers to tune in to matches and view them from the perspective of players, or from the perspective of a cameraman directing the action with commentators piped in. It all seems very similar to StarCraft 2's replay system, with the added bonus of it all taking place live. The spectating tool is currently only available as a standalone application.
This represents Valve's latest move in positioning Dota 2 as a powerhouse in the eSports industry. First came their million dollar tournament, The International, then came their documentary project, and now an overhaul of the viewing experience for eSports fans. Looks like Dota 2 and League of Legends could be gearing up for the next great eSports war.