I preordered both Diablo III and Heart of the Swarm, but Amazon keeps telling me they don’t know when Heart of the Swarm comes out. I’m rather curious to know, since DIII has been released.
Christmastime? That would be good, since my wife is out of town for two weeks 
Blizzard hasn’t officially stated a release date yet, but it’s expected this year. My guess would be a holiday release as well.
I’d expect somewhere between Diablo 3 (May) and the Mists of Pandaria WOW expansion. (Unknown, probably November or December.) Blizz usually announce their release date about 2-3 months before, so I’d expect somewhere around September-October. If MOP gets fast-tracked to September, then I’d expect HOTS right before Christmas.
Guesstimation, of course. The real answer is, as always, “when it’s done.” 
i heard it is too come out 3 days before christmas
Looks like Blizzard’s fiscal year ends with the calendar year. Since I’m not seeing any promotional activity for HOTS and they’ve just released both a full game and a new expansion pack this year, I’m revising my expectations for first quarter 2013 to boost their 2013 fiscal year. (With either another WoW/Diablo 3 expansion pack in the summer hols and then a Titan beta at the end of the year to boost expectations for 2014.)
I think we’re too late now to have the game out by Christmas. I’m expecting first quarter 2013 at this point.
Bliz started the HotS beta about a month ago. They’re gradually letting more people in, the way they handled D3 beta invites. No announcements about the end of beta or the release date, yet, of course. People wanting an invite need to make sure to opt in via their battle.net account screen - then clap your hands three times and say, “I do believe in fairies!” (Ok, maybe not that last bit, but it can’t hurt.)
I would guess 6-9 months for the beta test.
ETA: Bliz announcment
Looks like first half of 2013 is their aim right now. sigh
March 12th 2013.
It’s official, baby.
So, two years and eight months between Wings of Liberty and the Heart of the Swarm. I’d like to punish them for spending bloody ages getting the thing out, but the fanboy in me just knows that isn’t happening. (A courtesy that could also be extended to Valve, you know. You hear that Valve? Say something! Anything! I forgive you!)
Does anyone know what the deal is behind this expansion? It’s like a year later than everyone expected and those leaked timelines indicated. Is it 'cause League of Legends is murdering SC2, like I’ve heard?
It’s because the leaked timelines were really just total guesses, and Blizzard, as always, is ready when they’re ready and takes their time.
I’d expect the delays in the Diablo 3 development delayed HotS as well. I imagine Blizzard is large enough to support multiple teams, but expect that Battle.net and net-code is its’ own team. When they suddenly needed to do a lot of extra work on that platform to support Diablo 3, they couldn’t do the work they were supposed to do for HotS. So Diablo 3 gets moved up a bit, but Mists of Pandaria remains on schedule, so they’d be forced to either squeeze HotS in the middle or put it out for the christmas season. Leaving them with a fairly content-empty 2013 calendar.
ETA: Scuttlebutt has it Blizzard were caught unawares by the amount of work needed to support the D3 auction house and they got a lot of feedback after the D3 beta.