GameGuide

Professions
Increasing Nitro Boots duration to 5 seconds
That is an option we may explore. We also have several other changes to Nitro Boots in mind. We may include additional stats to making this comparable to other boot enchants. Many ideas are currently on the table and we are narrowing them down to the very best. I hope that not too many of my fellow engineers dropped the profession because of this change. Cool things are on the way. Hang in there. (Source)

Player vs. Player
Water in arenas
There used to be an effect on Arena water that prevented it from really kicking in until about 4 sec or so. Somewhere along the line that stopped working, but our intent is to get it working again.

The buff was mostly so casters didn't have to spend so much time on regeneration in between pulls or when soloing. If we had not buffed Arena water, then mage water would have been too good, and if we had not buffed mage water, then a core mage ability would be bad. The solution is to make water work like water, but make any water less uber in Arena. (Source)

Consequences of nerfs in PvP
In PvE, if we nerfed a class by 5%, you might find that the class representation drops slightly. In PvP it's a whole different ball game. Teams may choose to use other classes. Players who were dps spec may choose switch to healing. If a class is nerfed, the class it countered may suddenly rise. Balancing classes in PvE is like adding or removing helium from a balloon. You can make it go up or down a little. In PvP, all of the balloons are connected together through complex webs and you're doing the tweaking in a wind tunnel. That's not a cop out saying that PvP can never be balanced, but is instead my counter to the argument that "because spec representation rises and falls to such a degree that the changes are too extreme." Even small changes can have extreme results in PvP. (Source)

Itemization
Regen Stats
The solution here, from our POV, is not to take the regen stats off of gear, but to get you to care about them. To us, that's the same argument as saying "I can get all of the hit I need through talents, so hit on gear is a waste for me. Please remove it."

Using Leather armor instead of Plate as a DPS
I addressed this recently. The root of the problem is that putting AP + Strength on plate feel dumb (because except for block, it's the same thing). Putting Agi + Strength on plate feels useless. A long-term solution would probably be something like letting rogues (and similar classes) derive AP from 2xAgility and just put Agi on leather and Strength on plate. (Source)

Dungeon itemization and badges
I'll just comment on one point you made. In BC we felt like the system pushed players too hard into running the 5-player heroic instances long after they could benefit from the gear in order to farm badges. In LK we totally did away with this (since badges themselves are tiered) and also got rid of attunements and made Naxx relatively easy. As a result, I agree that we let end-game focused players graduate from heroic 5-player instances too quickly. In the future, we'd like to strike a more even balance where it might make sense to run a 5-player dungeon on a non-raid night, but you didn't feel obligated to every night. (Source)

Classes
Spellpower Cap?
At this point in time there is no cap on spellpower nor do we intend to introduce one. (Source)

Dual-Spec
The purpose of dual spec was not to make talent choices irrelevant (because you'd only have a talent in the cases where it was most useful). The purpose of dual spec was to make it less painful in those situations where you often switched between two commonly-used specs. This is the reason we placed so much emphasis on remembering action bars and less emphasis on the gold-saving aspect of the respec.

You won't see more than two specs for a long time, if ever. Let's see how the first one plays out for more than 6 weeks first. (Source)

Tanking in PvE
Traditionally, bosses hit almost entirely through physical damage and then occasionally threw in a big magical hit. The magical hits were scary because they couldn't be blocked and went through armor, so the only things you could do about them was burn a cooldown or heal like crazy. Fortunately the magical attacks cannot crit so at least the damage, while large, could be predictable.

Block was a fine stat back when bosses could do Crushing Blows. In their absence, it does feel like it has slipped as a source of mitigation. We (the developers and the community) were worried at the launch of Lich King that block would make warriors the best tanks, paladins second, and everyone else far behind. In retrospect we should have been more focused on the cooldowns and number of hits a tank could take in a row. (Source)

Balancing PvE encounters for each class
You know, those encounter designers are right across the hall here. I am waving at them right now. We all work pretty closely together to match the boss abilities to class abilities. We work even closer together on the numbers. When someone is tuning Frozen Blows or Imbalancing Strike, they do that knowing what the stam pools, mitigation, avoidance and cooldowns are of appropriately geared tanks.

That's not to say boss design is irrelevant. Say for example we made a raid with one boss, like Eye of Eternity. Now say Feral druids were slightly better at that fight. Does that mean druids are overpowered for that encounter?

There are 14 Ulduar bosses. If DKs are better at tanking 5 of those does that mean DKs are overpowered? If the next tier of content has bosses that druids are better at tanking, does that make things equal?

We want them to all be close ideally. …