The teaser trailer for StarCraft II: Heart of the Swarm launched over a year ago (longer for the first details), and ever since the information has been coming in bits and pieces. Recently, Blizzard announced something that is sure to make everyone excited, as the multiplayer beta for Heart of the Swarm will be arriving "very soon." The blog post on Battle.net states the first wave of invites will go to some of the players that assisted with Patch 1.5 for StarCraft II and some pro-gamers and press. More invites will be sent out later on, but Blizzard wants the select group in first. The HotS beta is multiplayer-only, but I do not think that is going to deter anyone from hoping for an invite.
In order to possibly be selected for the beta, the studio says you should make sure you opt-in on Battle.net. Simply go to your "Beta Profile Settings" on your Account Management page and click on the StarCraft Universe one. It does not guarantee you a spot in the beta, but it certainly improves your odds. Blizzard will also be partnering with fansites and "community personalities" to hold contests for beta keys over the coming weeks, so you can try to win one that way.
The multiplayer beta is a good step towards the eventual release of StarCraft II: Heart of the Swarm. Hopefully it is not too long before we learn what the Queen of Blades is up to with all of her spare time. Before then, I know many people will be constantly checking their email for a Heart of the Swarm beta invite. Just try not to crash anything.