I hit level 80 at around 5pm on Saturday and then started running heroics an hour later when more level 80 guild members logged on. I might have rushed through 79 for the sake of catching up with everyone >_<. Instance completion is retroactive in the sense that, if you run heroic before you run normal mode for a particular dungeon, credit for both achievements will be given.
Don't forget to pickup a reputation tabard before you start doing the high level dungeons. I want my Red Drake Mount, which requires exalted Wymrest Accord (I am 5929 into revered at the moment). There are three daily quests for that faction: One at the Wyrmrest Temple and two in Coldarra, each giving 250 reputation a pop (275 for humans).
I intend on farming HUK every damn night until those DPS pants drop. Oh, I'm still retribution spec by the way. I don't plan on specing back to protection until there is a need.
- Heroic Utgarde Keep is the easiest of all the heroic 5-man dungeons. The difficulty is about the same as a standard level 80 instance, easily doable in entry level 80 gear. I don't think that there was anything different about the encounters in comparison to normal mode.
- Heroic Nexus: A little harder. We ran into a few problems with Keristrasza and her enrage eating the tank (most of us had pretty much, just hit 80 and were in half-assed gear). There is an additional boss in heroic mode, just about where the quest book is found. Kill or control the adds, stay out of whirlwind.
- Heroic Violet Hold: Fairly easy. If you get Xevozz, remember that if the orbs touch him, he gets a mega buff and will start one shotting people. Just kite him in circles around the room (up the ramp and down the other, repeat). Casters and healers might want to pre-position themselves, to make sure that they won't go out of LoS, since the tank will be continuously moving. I'm not sure if the teleport is random or line of sight related.
- Heroic Drak'tharon: We couldn't do King Dred. We are either missing something strategy wise (the bleed eww) or just hit a gear wall.
My very first level 80 epic!