What does the tooltip mean for the Traveler's Tundra Mammoth where it says it carries vendors?
It means just that! It comes with two vendors. One sells reagents (including poisons) and the other sell trade supplies, like thread and parchment. The trade supplies vendor also sells some statless fashion clothing.
If you're not using the vendors and want to let your buddies hop on, there will be an Eject button to throw the vendors off and make room for your friends. And yes, only people in your party or raid can get on your vehicles. No random strangers will be jumping on your mammoth or motorcycle.
Can you suggest the best enchants for a Death Knight fresh from the starting zone?
Other readers were exactly right. Death Knights will be using Warrior stats for the most part. Strength, Stamina, maybe Agility if you have a lack of better options for a DPS set. Again, as other readers stated, don't worry about weapon enchants too much. Death Knights have Runesmithing (engraving runes into their weapons for various effects) that takes the slot of a weapon enchant.
When an enchanter puts the enchant on parchment and then on the Auction House, will they have to have the mats to create the enchanted parchment, or will the person purchasing the enchant have to provide the mats?
The Enchanter uses the raw enchanting materials to put the enchantment on the parchment/vellum. The person who purchases it on the Auction House just uses the enchanted vellum on their gear. So the enchantments would be on the auction house for the materials cost + crafter's fee, depending on your server.
About Druid's flight form: can they fly in Northrend without cold weather flying? I'm guessing no, but...
They need Cold Weather Flying just like everyone else.
Do they get it like everyone else (buying/training) or is there a specific druid quest for it?
They need to train it the same way everyone does, yep.
With the passenger mounts how will aggro radius be affected? Will your lower level passengers still aggro like normal?
Everyone on the vehicle has their own aggro radius. While the vehicle itself takes falling damage and not the people riding it, everyone riding it can be targeted by mobs and other players. If you take a level one character through Icecrown, they are totally screwed. This also has some hilarious consequences. If you take your passenger into an area you have progressed via phasing to have no mobs for you, your passenger may not have done those quests yet. You would be completely safe partying with dancing leprechauns that are throwing streamers while your friend is being assaulted by horrible twisting flesh giants with gaping maws and thrashing tentacles.
And yes, if you leap off of a cliff with them in your vehicle and dismount, you will all fall to your doom. Daze doesn't seem to do anything to anybody, however.
Will the passengers of the multipassenger mounts be able to get off whenever they want or will they be stuck on the mount tell the driver dismounts?
You can get out whenever you want.
My question for the beta testers - What are the passanger mounts acutally for? Why would anyone want to spend 20k on them? Apart from bussing around pre-lvl30 characters, whats the benifit of them? Everyone at least now has an epic ground mount, so why would you want to be a passanger on a motorbike or Mammoth?
What is it that makes it worth 20,000 gold?
This is largely going to be an opinion answer, one that varies from person to person. Not everyone will have one of these, but some will. It might be worth it to one person but not the next. The fact that it comes with vendors is pretty amazing. No matter where you are in the world, you can step outside and restock reagents, or poisons, or pick up some basic crafting materials. That's pretty cool. You can also use it as a better version of auto-follow. If your friend is going AFK, he can just hop on your mammoth and you can get going to your destination, or vice versa. In PvP, your entire party (most of it) can roll up on a huge Mammoth and descend on your opponent all at once. That's pretty neat, and intimidating! If you're a roleplayer, you can have your friend jump on your mount and you can take them for a spin. Cruise for chicks on your fly ride! Or make out in the back seat. You know, if you're into that kinda thing.