As Massively referenced in their post yesterday about DC Universe Online's concept art, the folks at SOE Austin are looking to change the playing field fairly substantially with their superhero MMO title. In fact, in a number of ways they're looking to re-examine a lot of the basic elements gamers think of as part and parcel with the MMO package. One great example is the concept of questing. Your average experience in a massively multiplayer game right now involves seeking out quests - essentially 'todo lists' - from characters a story-centric quest hub somewhere in the game world.
In DCUO, the goal is to let players do what they want to do with the time they have in-game. To that end, the designers are seeking to push content on players, rather than make players seek them out with their precious game time. Calling them 'encounters' rather than quests, these experiences are totally changeable based on developer intentions, and local conditions. DCUO offers traditional questing as well, with well-known quest givers and amazing quest content ... but they're definitely seeking something new in encounters.