I'm aware that most games have a function to share quests. Having lead pick-up groups in several MMOs lately, I've been in a position to see what other quests the people on my team had. Sharing wouldn't have done any of us any good, because never -- not even once -- did any two of us have even one quest in common. So I stand by what I said: we could be doing my quest, your question, person #3's quest, doesn't matter whose quest we do, only one of us is going to get the quest completion bonus at any given time.