It is possible to form a raid and attack cities to kill the leader of it; in fact, it's part of the PvP achievements to kill the leaders of all enemy cities. This will award you with a special mount as well.
The Firelands instance will be one of the new raids in World of Warcraft: Cataclysm. It is going to be a 10/25 man raid meant for level 85's (the new max rank in Cataclysm). It will be accessed from Mount Hyjal.Fire elementals, Flame Sprites, Fire Mephit, Azer, Magmin, Fire revenants, Salamanders (elemental), Efreeti, and phoenixes will be included in the raid.
Currently (3/24/2010) there is very little information on the guild ranking system for Cataclysm. There is simply not enough information to make any sort of meaningful comment.
No, Chuck Norris is no a raid boss in World of Warcraft. However, some people think he should be.
A 40 man raid
A level 60 raid.
As of patch 3.2 the newest raid instance is Ulduar.
The newest patch in World of Warcraft is 5.4 Siege of Orgrimmar. Players at level 90 may do 4 new raids in raid finder, flex raid, normal, or heroic with items up to an item level of 566.
Both 10 and 25 man.
Malygos is the boss of the Eye of Eternity, the Onyxia-style raid instance in the Nexus.
An "Old God". The last boss of the Ulduar raid instance in Storm Peaks.
If everyone in your raid has at least an item level of 330+ you should only need 1-2 tanks, 1-2 heals, and 4-7 dps for Ulduar 25 so I'd say 8-10 people should do it easily. If everyone in your raid is familiar with the fights you might not even need that many.
You can since the last patch. :)