Alright, once you hit 80, your only progression concern right off the bat is normal dungeons and Heroic dungeons. Be your own judge of your gear, and decide when you're ready to hit Heroics. You don't need to be incredibly well geared for them anymore, but you don't want to be in all greens, either. I have quite a bit of gold in my pockets, so upon hitting 80 I just went to the Auction House and people with various tradeskills and commissioned some gear from them. My Protection Paladin was successfully tanking Heroics purely in BOEs about two days after hitting level 80 thanks to Tempered Saronite and Titansteel. If you're DPS, you even have more leeway than that. Just judge for yourself.
Once you've geared yourself up from Heroics, you can start raids. You have two options here. If you like keeping things small, you can do the raids on 10-man. If you like bigger raids, you can do them on 25. There are two versions of each raid zone, and you decide which you want to do. Heck, if you like raiding a whole lot, you can do them on 10 and 25, their lockouts are on a different timer.
There are also 'hard modes' of certain encounters. All that means is you do the fight in a different way, and it yields better rewards. For example, Sartharion is a Black Dragon boss underneath Wyrmrest Keep. If you kill all of the mini-bosses scattered throughout his zone, you can then fight him all by his lonesome and it's a very easy fight. If you do not kill the mini-bosses, they'll join him when you fight him and it's a much more difficult encounter. That's the hard mode. If you beat him on that hard mode, you get better loot.
As for Ulduar, no, you don't want to go in there in greens. You'll want Heroics and Naxxramas gear. I definitely believe people will still be running Naxxramas once Ulduar hits. There won't be as many groups as there are right now, but there will still be groups. If you have difficulty finding one... make one! Bug your friends, hit the realm forums to recruit, or whatever you need to do. WoW is a game where taking the initiative really pays off. Once you've done Naxxramas a few times, you'll be ready to hit Ulduar.
Ian R asked...
"Do you have to beat the old Vault of Archavon to get to the new one?"
Adam fielded this question yesterday... but I have a better answer, so poopoo on him!
All that they did is add a new hallway onto the existing Vault of Archavon. You do not need to kill Archavon to get to the new guy, you just take a right turn before you reach him. It's possible there's some summoning or unlocking process, but given the mechanics of Wintergrasp, I really doubt that. Making it a long process when you need to rush through it while you hold the zone would be... unwise.
"Dual spec question... is there a cooldown after you switch spec? If not, will dual spec become a quick 10 sec method for restoring full mana and health? Just switch and switch back."
There is no cooldown, but it most certainly will not be a quick method for restoring mana and health. Switching your spec drains your entire mana pool, so unless you like running around at 0 mana, you won't be switching specs for that purpose.
"I remember back before 3.0, no matter how much +hit rating you had, you'd always have a 1% chance to miss an attack or spell when you're hit capped. I heard they got rid of this and you can now hit 100% the time instead of 99%. Is this true?"
Have questions about the World of Warcraft? The WoW Insider crew is here with The Queue, our daily Q&A column! Leave your questions in the comments and we'll do our best to answer 'em!