There are 5 Gateways to the Emerald Dream: Seranade(Hinterlands), Dream Bough(Feralas), Bough Shadow(Ashenvale), Twilight Grove(Duskwood) and Crystalsong Forest (Northrend) , guarded by Elite Green Dragonkin and Green Drakes lvl 62.

Few months before Retail, Tigole[Jeff Kaplan] commented about the Emerald Dream, which he confirmed was looking great (June 2004):

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Tigole: “Actually, we have some pretty cool stuff planned for druids. They will definitely have a link to the Emerald Dream. There’s also a zone on the way to the peak of Mount Hyjal called Moonglade that will be very core to druid characters. Our *master of Warcraft lore*, Chris Metzen, is never short on ideas when it comes to the druid class. I was running around the Emerald Dream last Thursday… you guys are in for a treat. The level designers are doing a killer job.”—06 Dec 2003

Tigole: “The Emerald Dream is shaping up to be extremely cool. We don’t want to preview any of that content yet as it is *endgame* and we want some surprises for players. The zone is massive and beautiful. And once the content team is done with it, it will be exceedingly challenging >=]”—06 Dec 2003

Nethaera: “As for the Emerald Dream, there are no plans for anything as of yet but it is a consideration for the future. The Emerald Dream opens up a lot of different opportunities and the Burning Crusade is definitely not going to be the last of the expansion packs. There are many different places and story lines that can be pursued. The story is going to keep growing and as it does so, people will get to experience it.”—09 June 2006

“The Emerald Dream is the primal heart of Azeroth. It is a kind of echo of what the world would be like if intelligent beings had not altered its surface. The lands are inviting and pure, with rolling hills, dense woodlands and vast prairies filled with living creatures enjoying complete freedom. Even the mountains, such as they are, contain lush vegetation and peaceful valleys.”

Personal Analysis

Some fans believe the Emerald Dream has existed since before the Titans arrived.  Others say the Great Sea and the Maelstrom exist in the Emerald Dream.  However, both thoughts are incorrect.

“This is a place where no elemental walks, where no great power ever altered the terrain. A paradise, indeed.”

• This clearly says the Emerald Dream exists far after the Old gods and Elementals were imprisoned. “No elemental walks” means no chaos exist anymore. The Titans bring order to chaos in the universe. Taming the elements and crafting an athmosphere that may spring life such as paradise.
  
  

• No great power ever altered the terrain: The Burning Legion devastated the Barrens, Suramar and cursed a section of the Moonglades now known as Felwood. This great power “Burning Legion” altered the terrain.
  
  

• The Emerald Dream is Azeroth if intelligent beings hadn’t existed: Humanoids such as Trolls, Night Elves, Humans, Taurens, etc.  Where only the trees, plants and animals roam.  The Highborne Elves created Zin-Azshari and many cities out of wood and rock, twisting and reshaping the terrain with arcane magic to take the shape of their glorious cities.  The Emerald Dream doesn’t have any of those buildings or alterations on terrain created by intelligent beings. Therefore, the Sundering, Maelstrom and the Great Sea shouldn’t exist in the Emerald Dream.

All this analysis is based on quotes from the Official Site Lore:

“The Titans, colossal, metallic-skinned gods from the far reaches of the cosmos, explored the newborn universe and set to work on the worlds they encountered. They shaped the worlds by raising mighty mountains and dredging out vast seas. They breathed skies and raging atmospheres into being. It was all part of their unfathomable, far-sighted plan to create order out of chaos. They even empowered primitive races to tend to their works and maintain the integrity of their respective worlds…

the Titans brought order to a hundred million worlds scattered throughout the Great Dark Beyond during the first ages of creation.

... For many ages the Titans moved and shaped the earth, until at last there remained one perfect continent. At the continent’s center, the Titans crafted a lake of scintillating energies. The lake, which they named the Well of Eternity, was to be the fount of life for the world. Its potent energies would nurture the bones of the world and empower life to take root in the land’s rich soil. Over time, plants, trees, monsters, and creatures of every kind began to thrive on the primordial continent. As twilight fell on the final day of their labors, the Titans named the continent Kalimdor: “land of eternal starlight”.

“Suddenly, ahead of him lay a huge, black lake. Malfurion frowned, certain that he recognized the foreboding body of water. Dark waves lapped the shores and an aura of power radiated from its center.

The Well of Eternity.

But if this was the Well, where was the city? Malfurion eyed the dreamscape where he knew the capital should have been, trying to summon an image of it.”

When looting Eranikus after killing Jammal in the Temple of Atal’ai in Swamps of Sorrow, he drops the Chained Essence of Eranikus trinket.  Take the trinket to Itharius, at the cave located southwest of Swamp of Sorrows.  He will give you an Oath rune.  Upon acceptance, the trinket is removed from your bag and you become an agent of the Green Dragonflight and Ysera.

Itharius sends you to meet Umbranse the Spiritspeaker, a human,  located in Northeastern Winterspring.  He says that Eranikus isn’t truely dead, and he could speak and help him, but a powerful augur device he needs to help Eranikus was stolen against his will.  No one has been able to find the Augur device required by Umbranse.

In recent quests after the War Effort to open the Gates of Ahn’Qiraj, in order to create the Scepter of the Shifting Sands to bang the gong, you need to gather the pieces of the shattered scepter from 4 dragons that guard a piece.  One of them is Eranikus the Corrupted.  Eranikus is summoned in Moonglades with help of Remulos - son of Cenarius.

Eranikus the Corrupted claims to serve his god.  This triggered the rumor that the Old god C’Thun is behind the Nightmare of the Emerald Dream.  Hints of this lead to think it is true.  That the Old gods are behind the corruption of the Emerald Dream through the Nightmare.

The introduction of the 4 Corrupted Dragons as outdoor raid-bosses, and later the introduction of Ahn’Qiraj Instance seems to point to a very soon release of the Emerald Dream instance.  The page will be updated when such time comes.

One of the four corrupted outdoor-raid dragons drop a corrupted signet ring.  When you bring it to Remulos in Moonglades, the dream-form of Malfurion shows up and reveals that he and Cenarius’ spirit are fighting the Nightmare inside the Emerald Dream. Malfurion hints the Old gods are behind the Nightmare:

Malfurion: “I fear for the worst, old friend. Within the Dream we fight a new foe, a born of an ancient evil. Ysera’s noble brood has fallen victim to the old whisperings. It seems as if the Nightmare has broken through the realm and seeks a new host on Azeroth.”