I think there has been a problem with the spawning of bosses. Folks are just waiting to see the spawn and had been camping to wait for them in specific locations. Since it's limited location is a problem, I think a simple information should be adjust to "Evil has arisen in the land." and XXX has eradicated the evil. no specifics to which boss has spawned and thus more time for every player to discover what evil has taken place. Naming the bosses only give us seconds to respond and that just isn't gameplay anymore, its just giving more to those that already have it.
I further would suggest that when a boss spawns, the previous boss would disappear unless it is being fought, and as soon as the fight cloud is gone if the boss is still alive have it give an evil laugh before it goes back from whence it came. A spawn might only last for 15 minutes or so before the next one does and I think the combination might make for better storyline later as well.