Information about specific achievements can be found at Achievements - Character
Split from the general Wrath thread, here is what Tigole had to say here regarding various posts that were talking about achivements.
On Tuskarmageddon (kill a million tuskaar)
The achievement is just an internal joke and I never deleted it. It would be a horrible achievement. It will go away someday, although I love the name...
On challenging dungeon & raid achievements
The challenging achievements in the Dungeons and Raids area aren't fully flushed out yet. They are coming. Because we're still tuning that content, it's hard to come up with what would be the "perfect" raid achievement. Examples from TBC would be, "Kill Moroes with the 4 adds still up", "Kill Hex Lord with his adds still alive", "Kill Blackheart in one charm or less" etc... The Dungeon and Raid achievements thus far are what I'd consider to be the "base layer" with the more interesting ones still being developed and implemented.
On Sulfuras' Feat of Strength not showing up if you deleted the item
Atiesh and Thunderfury are retroactively awarded because those items are based on quests. Sulfuras is not retroactive because there isn't a quest for the final item. But if you have the item on your character (bank or in inventory), you'll still get credit.
On kill achievements
Straight-up kill achievements are not retroactively awarded. I know what a bummer this is but we can't track that information efficiently.
Also, there is no more 40-person Kel'Thuzad in Lich King... only 10/25.
On legacy content
I agree that there's not much achievement in killing the old bosses. But I think it will feel better for new players and re-rollers to have those achievements in place from the get-go. Also, an important thing to remember is that achievements now track the date. Eventually, the date will become the meaningful piece of information and give validity to boss-kill accomplishments.
Regarding the points, they are entirely placeholder at the moment. We have a lot of tuning to do in order to get the points just right, so feedback on which achievements should be worth more/less is really valuable.
I'd love for achievements to get its own thread here but it seems like you guys make new threads about as often as we make new games...=P
The secondary skill achievements are in their own category, not parts of Feats of Strength.
On what Achievement Points actually do:
Right now, they only give cosmetic rewards: titles, tabards, vanity pets etc.
There is the possibility that we will do some attunements based on this system as well or that we will add some minor benefits such as consumables but right now the thought is that achievements are recognition of your progression, not the means of progressing.
Also on the wow forums regarding character vs account achievements: WoW Forums -> Achievements which is it?
For now, they are by character. Eventually, our plan is to expand these to account-wide achievements. More details to come in the future. For launch of Lich King, however, they will remain at the character level.
Daily quests don't count: WoW Forums -> Not enough quests to complete achievement?
Daily quests and repeatable quests should not add to cumlative zone total achievements. It should only count quests that you can complete once.
Armory features are planned at some point. WoW Forums -> Achievements and armory?