World of Raids has an extensive set of posts up on its forums chronicling the events surrounding Blizzard's public testing of the Battle of Mt. Hyjal. As expected, different members of the forums had different screenshots of the battles they went into, with some of them providing video of the encounter as well.
Currently, it seems Rage Winterchill is the first of the five big bosses set up for the encounter, though he's only appeared as a result of a GM summoning him into a raid. Naturally, players were thrashed either by Winterchill or by the waves of increasingly difficult mobs that periodically made their presence known to beleaguered players.
World of Raids has more screenshots up for people to peruse from different players' perspectives. For now, you can view one of the sessions through this captured video of the event, with waves of undead slowly besieging Jaina Proudmoore through sheer numbers.
