I just wanted to clarify something that was said. Shipwreck mentioned that using codes for Summer of Arcade games won't get you the free copy of Crimson Alliance. This was true for previous promotions, but not for this one. XBLA Fans
went asking a couple of weeks ago and got the info on it. There was also some discussion between them, XboxSupport, and someone I follow on twitter a few days ago. At first support didn't seem to think codes would work either, but they checked and confirmed that they do indeed work. I'd dig up that tweet, but it was like 5 days ago which means I'd have to dig through like 3,000 @xboxsupport tweets to find it.
Most likely this is because the Microsoft Store was selling codes for SoA games this year. The XBLA Fans info says that codes that went out for review and given away in contests should also work.