Need clarification on what is getting changed

Q u o t e:
So explorer and Loremaster are becoming Feats of Strength?
Is MC and BWL getting destroyed along with Thunderfury becoming unobtainable?
Can we still get the 'What a long strange trip it's been' in Cataclysm?

The exploration and quest achievements probably won't change. If you have the achievements, you won't lose them. If you don't have them, you can still get them, but obviously you'll have different quests or areas to explore. The greatest risk is to players who are almost done with one of these achievements, because they might suddenly have to do more than they thought (say 100 quests instead of 50).

We aren't removing MC or BWL as of this writing. We aren't going out of our way to remove old legendaries. The only risk there in a case like Thunderfury is if we change a zone like Silithus so much that the quests become hard to keep intact.

You can still get "What a Long Strange Trip It's Been." In general, we are going to go bend over backwards to not remove existing achievements.

Q u o t e:
What about achievement rewards like Glory of the Hero's red proto drake? As players get stronger in Cataclysm, achievements like that one will become very easy. Would it make sense to retire the reward to honor those who completed the achievement in its glory days?

This is all tentative and could change, but we don't really have a problem with protodrake farming. What we will probably do with really unusual mounts like Mimiron's Head and Invincible is make them a rare drop. The 100% drop rate won't make sense when you can overpower the content.

If you want to overpower the content for a drake though, go for it. Players who did it "legit" had the benefit of having the achievement and mount earlier than anyone else. The most prestigious mounts will change in Cataclysm.