The team reevaluated the previously announced 600-member cap and decided to increase it for patch 4.0.1 and Cataclysm.
A few days ago, Blizzard announced that a single guild will only be able to have a maximum of 600 members in Cataclysm. Well, the team reevaluated that number and just announced that the hard cap will be 1,000 members with patch 4.0.1. The cap is necessary due to the new guild system that's coming in the expansion.
Guilds with more than 1,000 members will be able to proceed at that level for as long as they want, but they'll have to drop below the 1,000 mark to add new members to the guild. So what do you think about the new cap?
A little later in the thread, Bashiok confirms that Blizzard would like to add features like a guild alliance chat channel in the future.