This topic is covered extensively in the FCM thread.

To me, however, it is DL making good on its promise to shareholders to have more paid seats in F. They just didn't specify just how cheaply they would sell the seats. Works out for me though, as I tend to receive multiple offers for <$100 RT, all of which I am more than willing to take for the SDC ability alone. Doesn't hurt either that I am only GM, and would never sniff an upgrade on the routes/times I fly.