Vaneras has revealed a few details about the upcoming new 25-man raid dungeon: PTR Ulduar It will be partially available on PTR at some point in upcoming weeks with various hard-modes to tackle. Blizzard is satisfied with how the Sartharion dungeon was designed and plan to create new dungeons with many hard-modes. Ulduar will not be just for everyone. Even in normal mode it will be challenging. It is developed for those guilds that have geared up through Malygos, Naxxramas and Sartharion, yet those will find WoW PTR Ulduar a hard experience..

Vaneras: Ulduar will be available on PTR in the future, however we are planning on having several limitations in place so that we can control what can be tested at any given time. Ulduar will also not be available permanently like Naxxramas was in the WotLK Beta.

All this basically means that if there is something we want to test, then we will enable the zone and encounter so that it is available. If at some point there is something that we no longer want to test, then the zone will be disabled so that it is no longer available.

Keep in mind though, that there will be quite a few encounters to test in both the 10 and the 25 man versions, and there will also be a whole lot of "hard modes" and achievements to test.

We are quite pleased with how Sartharion and his drakes worked, so we would like to expand on that idea quite a bit in PTR Ulduar and future raids. We are currently planning for most of the encounters to have "hard modes" that will allow for raids to increase the difficulty. Increasing the challenge will of course also mean an increase of reward level if successful.

Daelo: Ulduar will be on PTR in the future, but we're going to have tight controls in place on what can be tested at any given time. Ulduar will also not be up permanently like Naxxramas was in the WotLK Beta. If we have something to test, we'll make the zone and encounter available. If we don't, we'll disable the zone.

That being said, there's going to be a LOT of encounters to test in both 10 and 25 player modes. There will also be a whole lot of "hard modes" and achievements to test. We're shooting for most all of the encounters to have "hard modes" that allow raids to increase the challenge and reward level if they're up to it. We're pretty pleased with how Sartharion and his drakes worked, and we're going to expand on that idea extensively in Ulduar and future raids.

The reward for completing the hard modes are not going to be just achievement points, titles, or mounts, but improved, additional item rewards.

I think it's safe to say that Ulduar will be a bit more difficult overall than Naxxramas, even without the hard modes. We're still going to tune the zone for accessibility(*), but a raid group that's done Naxxramas, Malygos, and Sartharion and obtained the gear from those encounters should be well prepared for Ulduar. Not only is the raid's gear better, but players should now have some raiding experience under their belts. We also have a much more accurate picture of what guilds are capable of from a healing, damage, and tanking perspective then when WotLK first went live. If Naxxramas was the introduction to raiding 101 class for players who have never raided before, think of Ulduar as the second year class.

* There will be one optional encounter that is only tuned as a "hard mode" encounter.

I don't think you have to worry about spoilers from Achievements, to be honest. Seeing achievement text before you fight a boss is like seeing a single piece of a large jigsaw puzzle. Sure, it's something, but it's nothing really without seeing the context of the encounter as a whole. I also expect achievements to be something tested late in the PTR process. Implementing them is one of the last parts of the development pipeline.