The servers are "full" because a specific section of Ul'dah (the front area near the teleport crystal) has in the past been consistently overcrowded causing tons of crashes and server issues, since it was where a majority of the population would stand afk or gather together. They added quite a bit of stuff this last patch to spread the population out to other cities and other sections of Ul'dah and are monitoring it to see if the situation clears up.

Hopefully we get an update on it soon because we also have some friends that want to play.