Although I don't have a full grasp of the upcoming guild rep stuff, I absolutely LOVE the idea that guilds will get rewards (perk system) for their team work with reputation in Cataclysm.
I can absolutely see this portion of the game becoming a very hip thing and that guilds will be created just for getting the rep built up and reaping the benefits of mounts or tabbards or whatever other goodies that Blizz has in store. Perhaps guilds would promote a Rep Leader to coordinate days and events to build reputation for the guild. Almost like a whole new job:)
There are so many possibilities for this aspect and if done well, it could perhaps open doors for those that are more serious pver's within a guild to group with those that are not so serious to complete quests or whatever task it may be as a group. I would love to see some really fun goofy cheeves put in for guild rep. Perhaps drinking until its all a blur then winning an Arathi Basin match hehehe. I know I know, I'm a goof.
I do hope it isn't all too serious and that there are lots of fun elements combined in this to really pull guilds together. I'm excited about the prospects for surSave Nowe.