Blizzard has released its official Ulduar preview, available here. I’ve distilled down the important points for raiding as well as a reflection on my previous information leak:

• The number of encounters as well as the information about an entry “wing” from my leak source proved almost correct. That means the rest of is most likely close to correct. Check out my original post Preliminary Ulduar Info Leak for the details. Summary: one “arena” style encounter where you fight four bosses at once, a final wing similar to the Frostwyrm lair that won’t be seen on the PTR, one hard-mode-only encounter.
• Ulduar is a prison for an Old God. What this means is that the final area (similar to Frostwyrm lair) will most likely be the actual prison itself, while the rest of it will basically be fighting through the defenses or wardens of the prison (”Iron Army”).
• It’s hard to tell from the wording, but it seems like the initial area will be a large open area in which you will pilot vehicles and have to clear our a lot of trash (Iron Army stuff) to get bosses to spawn. This may be vaguely like Hyjal in that you’re in one fixed area (although probably much bigger with a lot more movement) and the trash and bosses come to you.
• The fact that the initial area is so vehicle dependent means your gear will have very little impact on your ability to progress through it. This is a plus for those guilds who haven’t had as much time to farm up the gear.
• As I suspected, they are heavily leaning on “hard mode” versions of encounters similar to Sartharion to satisfy both the needs of accessibility (easy content for the masses) and challenge (difficult content for power guilds to measure themselves by). From the wording it seems like they have whole-heartedly embraced this as the new paradigm by which all raid content will be designed, and I think this is a huge boon to raiding in WoW.
• They’ve not only embraced “hard mode” content but also more granularity in individual encounters. I suspect that most encounters will either be “easy” or “hard” mode but at least one and probably a few will provide multiple levels of challenge similar to how Sartharion had four difficulty levels (0 drakes, 1, 2, 3).
• “Patch 3.1 will hit the Public Test Realms very soon”. When Blizzard says “very soon” that usually means within 2-3 weeks. If you’ve gotten lax with your raid schedule and you wish to be competitive when 3.1 hits I recommend you begin ramping back up in anticipation of the PTR. Get a post out on your guild forums telling people that they need to be ready to get characters copied to the test realms as soon as the copies come up. Preparation is the key here because if you’re slow out of the gate, getting copied to the PTR can take a very long time.

Get your horses ready! The gates will open soon.