I find it interesting that Dark Knights excel at tanking magic damage just like Death Knights did in WotLK, and in this and that, both of them were considered weak at first. But, Death Knights ended up being used effectively throughout the expansion, and because Blizzard buffed them since the community kept complaining, they ended up being completely overpowered.

Just, something to think about when you're talking about buffing and nerfing classes this early in an expansion.