| Stay dead!|
So, I was thinking about games like Metriod where you go into a room and shoot up a bunch of baddies then leave it for whatever reason, then you remember you needed to do something back there and immediately return. All the baddies are dead and stay that way until you go at least two rooms distance away.
How this relates to Guild Wars is, to help discourage some forms of farming, it would be interesting to see a timer added to the deaths of mobs, so that when you kill a creature and leave the area, it doesn't come back right away, but waits till you've gone for about a minute or two, or gone a couple maps away.
The other advantage would be for someone who has to go into a nearby map for a quest, then return to the previous map. It would lower the time necessary to complete the quests, as they wouldn't have to kill their way through all the mobs again before being able to return to their quest.
An offset that would help in this case would be smaller maps, or maps broken up into more areas that would count towards this timer, so people wouldn't get totally frustrated with the "Kill 50 Rats" quest.