The question of what Blizzard will do to tide over World of Warcraft content between now (patch 3.3, Fall of the Lich King) and next expansion Cataclysm appears to have been answered: stagger Icecrown Citadel's opening.
Released earlier this week, new raid Icecrown Citadel invites players to assault Arthas' - the Lich King's - home. But it now appears the game will not let you fight him until some time around April.
Blizzard has programmed the raid dungeon so that new wings open at intervals, and the first won't open until January 5th. Players can, at the moment, only fight their way up to the entrance where Arthas' most loyal Death Knight Deathbringer awaits.
After crushing his bones, a friendly faction hero will inform you there is a 28-day wait until the door to the next wing is battered down. If this pace is kept up, two further wings will open in February and March, and the Frozen Throne containing Arthas himself at the start of April.
Judging by the World of Warcraft websites the wings will open in this order: Frostwing Halls, The Plagueworks and The Crimson Hall.
Once all three are cleared, raiders will finally be granted access to The Frozen Throne, where Lich King Arthas and his closest aids await.
Icecrown Citadel may be the focus of the Fall of the Lich King patch, but it is by no means the only content within. The World of Warcraft website addresses each aspect in full.