Source: See below.
What we heard: Today at GDC Online in Austin, Texas, Battle.net project director Greg Canessa took the stage to talk about the future of the encompassing online service Battle.net. Following his presentation--a complete write-up of which can be found here--the former PopCap games executive took questions from the audience.
One inquiry may have led Canessa to tip Blizzard's hand about the release date of the first expansion to Stacraft II: Wings of Liberty, Heart of the Swarm. When discussing such future Battle.net features as trading replays, broadcasting replays, and upgrading profiles, he said they were "a main area of focus we're going to be seeing on the Starcraft [II] side over the next 18 months between now and Heart of the Swarm." (Emphasis added.)
Such a time frame would have the expansion arrive in either March or April, 2012. Heart of the Swarm is the second installment in the three-part Starcraft II saga, the first of which, Wings of Liberty, focused on the human faction. Heart of the Swarm will concentrate on the Zerg faction of the real-time strategy, while the third installment in the real-time strategy trilogy, Legacy of the Void, will focus on the sinister Protoss faction.
The official story: A Blizzard representative stressed to GameSpot that there is no announced released window for Heart of the Swarm. However, he did say that the game would not be featured as part of Blizzcon 2010, which will take place in Anaheim, California from October 22-23.
Bogus or not bogus?: Not bogus. Blizzard typically takes its time between expansions, as evidenced by the nearly two-year gaps between the World of Warcraft add-ons The Burning Crusade (January 2007), Wrath of the Lich King (November 2008), and Cataclysm (December 2010).