Membership Benefits (Gem-Stuffed Envelope)

Note, there are four different "Membership Benefits" quest entries on Wowhead. These are all the same quest, the only difference is the rewards given. These are related to your reputation level with the consortium. You receive a sack of gems that increases in value and number with each higher rep level.

Gem Stuffed Envelope appears to be for Friendly
http://www.wowhead.com/?item=25424#00zc

Unmarked Sack of Gems appears to be for Honored
http://www.wowhead.com/?item=25419

Bulging Sack of Gems appears to be for Revered
http://www.wowhead.com/?item=25422

Bag of Premium Gems appears to be for Exalted
http://www.wowhead.com/?item=25423

This is a reward from the consortium. It does contain gems, rarity is based on your current standing.

The "monthly" rewards is currently bugged, confirmed by Blizzard. It's on their list to be fixed in a future patch. At this time there has been no word if there will be "back-pay" or any other details on the timing.

Update: In patch 2.1 http://forums.worldofwarcraft.com/thread.html?topicId=94203802&sid=1 characters with reputation of Honored or higher can go to Gezhe in Nagrand to pickup their monthly payment.