There is a rule of thumb for online games saying that the population of a server is between 5 and 10 times the maximum concurrent users. In other words, even during prime time at least 80% of the players on a server are offline. Another observation for MMORPGs is that if you gather X players on the same spot, the amount of data transfered goes up with X squared, because you need to send the information of every player's location to everybody else around him. Combine these two effects, and you realize that making a "world event" at a specific time and place generally a bad idea. More players log on than the servers can handle, and players at the spot can't all see each other, or there is a lot of lag.
Blizzard gave up on such world events after the lagfest that was the opening of the gates of Ahn'qiraj. After that world events were stretched out in time and in space. Trion just learned this lesson in Rift's first world event, the River of Souls. Some players got stuck in a 5-hour queue and missed phase 2 and 3 of the event, as those only lasted for half an hour. Trion having scheduled a free trial weekend at the same time didn't help.
The solution to running such world events is at the same time obvious and impossible: You need to have server hardware that can handle a far higher percentage of players being online at the same time, and in the same zone. That is a bit like building a supermarket with 100 checkout counters when on your busiest day only 10 to 20 are needed, just in case all your customers come in at the same time. I wonder if in future with the advances of cloud computing it would be possible to have huge extra server capacity for specific world event days. Until then, world events tend to disappoint a lot of players.