Near our chaos stone there is a mob spawn that changes depending on the day/night cycle. During the day, the mobs are easier, while at night there is a chance a far more powerful version of the mob will spawn.
This resulted in some pretty cool player behavior in our clan last night. As soon as the sun started dipping low in Agon, the players farming the spot called it out on Mumble and most left the spawn. I think one guy must not have been paying attention, because he stayed and kept farming. He finally noticed when the harder mob spawned and dropped him in short order. A good laugh was had over Mumbled as he asked for a rez.
DF:UW is not the first MMO to have such a feature, but for a number of reasons it feels far more organic here, and reinforces the whole “living in a virtual world” feeling versus just jumping from one themepark ride to the next.