Something I have wanted for long but never seen, is quests with a loose time limit. Meaning that if you fail to meet the time limit, quest isn't lost, but gets more difficult. For example if you are to kill someone, after the time limit he meets some nasty friends.
Or if you are to find someone, after the time limit, he leaves for some other place, so you have to search for him in some new (undocumented ?) place.
