Quest for Shadowmourne the Legendary is only available in 25 man Icecrown Citadel raid and you also have to kill the Lick King to get it forged at the end of the quest chain. Good Luck on that Epic Journey! That sure cuts out the amount of people that will ever see that including myself since its a 25 man raid as well and i'm only likely if ever to see Icecrown in 10's.
If you want one good reason to 25 man raid Icecrown Citadel in patch 3.3, right there gazing upon that weapon is one good reason to slave away for quite sometime to try and wrap your hands around.
People will really mourne in envy you when they see you with it. What will you do to get your hands wrapped around your legendary? You know you want it right?
What would I do, hmmmm. If Zan my old fun ex Warrior buddy and former GM restarts playing WoW again and reforms the old guild back to 25 man's just a possibility I'll move servers and rejoin him. Just day dreaming, but thats what I would do. Doubt that will ever happen.