Got an email about this deal today. Fine print (below) answers some of the questions I've seen in this thread. Codes tied to XBLA account and deal ends 2/13.
*Limited time offer good only for named recipients of this e-mail who are legal residents of the 50 United States or the District of Columbia 17 years or older. To receive The Maw and R-Type Dimensions you must purchase a 12-month Xbox LIVE Gold membership from one of the links in this e-mail or from the Xbox LIVE Dashboard on your Xbox 360 console between 12:01AM on February 3, 2011 and 11:59PM on February 13, 2011, while supplies last. Microsoft reserves right to expire offer at any time. Offer cannot be transferred, redeemed for cash, or combined with other offers. Offer not valid on prior purchases. Limit one gift per person. Codes redeemable for each game be sent to the e-mail address tied to the Xbox LIVE account used to register for the offer within 6-8 weeks after the offer end date. Valid e-mail required. Any e-mail returned as non-deliverables will not be re-sent. After promotional 12 months, your membership will automatically renew to a monthly membership at the then-current price unless you change your renewal or cancel before your membership ends. Pricing details can be viewed in the Account Management area of your gamer profile. Sponsor: Microsoft Corporation, One Microsoft Way, Redmond, WA 98052.