Quote from: Mumper (Source)

The guild rewards you guys are seeing in game are not hooked up yet. Guild rewards have 3 requirements that must be be met before you can use them. First and foremost, they must be unlocked via a guild achievement. Let's just say, that for example, you need to complete the new guild achievement "We are Legendary" in order to unlock the Dark Phoenix. That achievement requires the guild to gain access to all 6 legendary weapons currently available in the game. (note that all guild achievements start on Cataclysm launch, so anything you have now will not matter, it must be done with your guild after launch)

So, let's say that your guild get's this achievement and thereby unlocks the Dark Phoenix on the guild vendor. At this point anyone in the guild can see the item on the vendor, but they will need a specific amount of guild faction to be able to purchase it. In this case, let's say exalted. Now, once you have the guild faction, you can purchase the item for its gold price. (prices will vary based on the reward)

I am using the Dark Phoenix and the We are Legendary guild achievement as examples here but you should get the idea. Don't worry, we wont be handing out all the goodies so easily. =)

Now the important part from all of that was the line "note all guild achievements start on Catclysm launch so anything you have now will not matter( e.g. not count), it must be done with your guild after launch".

That meant that all guild achievements are not going to count retroactively. That is still the case but with one exception now.

Quote from: Mumper (Source)

We are making a exception for this guild achievement. Any legendary items you have already earned will count.

That means now that "We are Legendary" will count stats retroactively. It wasn't really a big deal to me personally because I felt that limitation was in there because they might not have been tracking or been able to track some of the achievement stats that they are now implementing. It's kind of like what happened when achievements first came out and you noticed you only had half of Classic Dungeon Master even though you knew you had run them all before.

This is definitely a great thing though I doubt any other guild achievements will be counted retroactively. Blizzard, and I think guilds in general wouldn't want to skip up 5 to 10 guild levels Day 1 if everything were to be counted retroactively, but this one achievement seems fair.

The raid group I run with actually joked about keeping a guy at 49 Shadowfrost shards until Cataclysm against his will so we could have Shadowmourne count towards the achievement. I doubt we would have actually been mean enough to go through with it but now we don't even have to ponder about it.

The Cataclysm Beta is always evolving and nothing is set in stone but it is great to see a swift response to issues that arise