Quote from: Mumper (Source)

The new guild system UI will be active in the pre-patch but guild experience and guild achievements will be disabled until Cataclysm launch.

Quote from: Mumper (Source)

There is no concept of "Top 20 contributors" anymore. We changed that functionality many months ago. XP contributed to the guild comes from all members. Guild rep is always available no matter what amount you have contributed to the guild.

This was in response to a question about whether you would receieve guild reputation, if you were not one of the Top contributors of the day/week

I'm excited for this. Some may say its imbalanced because larger guilds might have an advantage but there are a myriad of pros and cons here. Don't be so quick to judge.