One of the unique things from EQ1's questing system was that quests could be done out of order. Without talking to the quest starter NPC, you could kill a mob and find quest items. You could then hold onto the quest item until you eventually figured out what quest it was for.
I found this approach enjoyable, as it allowed you to do the quests backwards if you wanted to and perhaps discover quests that you would've never known about. Also, you didn't have to run into town to pickup quests before going into a dungeon.
Any word on how questing will work in Pantheon?
I know they have the perception system, and in the demo videos, with the key being hidden behind a fallen rock, it seems that you may only be able to pick up the key if you are not on that specific step of the event. Which I understand. Certain quests may need to be done in order (as was the case in EQ1 too), but hopefully they plan to have plenty of quests that can be completed out of order as well.