Xbox Live Rewards. The official Twitter account for Microsoft's wing that incentivizes friend referrals and surveys with free MS Points has announced Achievement functionality is coming this fall. The problem is we don't exactly know what that means right now.
A tweet issued earlier today simply promises "a new way to earn Rewards based on your Achievements," coming this fall. We hope this means difficult Achievements will net us MS Points – we definitely deserve a bonus for earning all of the Achievements in Avatar: The Legend of Aang: The Burning Earth – but that's speculation until Microsoft gets back to us.
Update: Microsoft wouldn't go into specifics and instead offered us the following statement: "We don't have many details to provide at this time, but can say that based on our member feedback, we're constantly looking for ways to continue enhancing and improving our Xbox Live Rewards program."