This topic comes up because we are nearing the end of an expansion, and what happens at the end of an expansion? Well pretty much nothing. Raiding gets old, Arena Seasons ending, BG are uneventful, and Dungeons are a cakewalk among many other things. So what tends to happen is people get to know their guildmates much more because they are not as "busy" as they were before. People talk more and something that may happen is they realize that some people in the guild are like them and some are not. Of course, then some cliques start to develop where people always hang out with certain people and might end up not having space or time for others. These cliques although are great for people getting friendly with one another you have to be careful because they can break up your guild. When people get the attitude that they don't want others in on their runs and all that jazz.
Come Cataclysm this is even more dangerous because if you don't promote guild unity then with the revelation that 10 man guilds are going to be even more popular. Come the expansion these people won't think twice about breaking off and doing their own thing. So during this time I would suggest still doing things as a guild. If you are not doing the current raids then have nights to do something old school and make it fun. Make a day to do achievements. Do a guild free for all in the STV arena. Anything to do things with one another to keep that unity together. Then when that stuff is not going on people can do their own thing and they still have that freedom, but the guild is not going apart at the same time. Just something to think about as a lot of guilds may be "shutting down" for Wrath.
I'll leaving you with a little quote I saw on the Greedy Goblin
Horndreaper: Can I have some money plz I am saving for my epic flyer plz
Reply: I have hidden all my money on the beasts of Azeroth. Kill some to claim your share!
Horndreaper: Where do I kill the beasts?
Enjoy your Monday