While killing mobs in a dungeon that normally gives rep for a faction, for example: The Wyrmrest Accord, if I am wearing the tabard representing the Warsong Offensive, will I gain reputation for both Wyrmrest Accord and Warsong Offensive at the same time?
Contrary to the original description of the feature, you only get rep with one faction at a time. Personally, I think that's a better design. If you're working on a particular rep, you can still help friends out in random unrelated Wrath dungeons without feeling punished. If you only received half of the rep gains, you would still want to go to Violet Hold for your Kirin Tor rep instead of Utgarde Pinnacle, just for random examples. Going to Utgarde and getting half of the payoff just feels punishing. Feeling punished for helping friends sucks.
If you want to go half and half, you can just take the tabard off halfway through.
To clarify, so we're on the same page: In your example you would only gain Warsong Offensive reputation in dungeons, with the tabard on. If you took it off, you would gain Wyrmrest Accord reputation. Hm, in hindsight, this answer was much easier than my first one.
Had a question about Old World city guards, will their level be raised from 65 to 75 with he expansion? Or will it remain the same?
Just like with The Burning Crusade, guard levels in capital cities will indeed be going up with the expansion. Capital city guards are level 75, and Goblin guards are level 77.
Vinicius O. E. asked two questions...
Do we have new item suffixes like the ones added in BC like "of the Beast", "of the Invoker", "of the Champion", etc?
I haven't seen any new suffixes, no.
When will the XP needed to level from 60-70 decrease? When patch 3.0.2 is released? WotLK?
Patch 3.0.2 is when that change goes in.
Can we get some more information on daily quests? Where are they? How many are there? I believe it was already stated they reward about 30g per quest, but how hard to do are they? And how long do they take?
Yes. Everywhere. A lot. They're easy. They're short. That work?
In all seriousness, there really are a ton of easy ones. Regular daily quests, profession daily quests, PvP daily quests, whatever you want to do. There are a ton of them, and you'll find them all over the place. Icecrown, Storm Peaks, Grizzly Hills, Zul'drak, Dalaran, etc. My personal favorite is the quest where a panther god thing takes over my body and we go wreak havoc on some irritating badgermen.
Please tell me there is gonna be a AH in Dalaran!
If you're okay with me being a complete liar, then yes, there will be an auction house in Dalaran. If you'd rather I didn't lie to you, my answer will be different.