The Facebook page offer extends to new Galaxy S III, Galaxy S II, and Galaxy Note buyers. For example, if I was to offer my Nokia Lumia 900 (with proof of purchase of a qualified Samsung Galaxy device), I could get a rebate check for $200. The 16GB GMS iPhone 4S brings back the maximum $300, while an older model like the Samsung Focus will only bring back $35 in trade-in value. If you've upgraded multiple phones recently to the Sammy Galaxy line, like in the case of a family plan, you can submit multiple phones at once for trade-in.
Is it a good deal? As The Verge notes, it's a so-so offer at best, but a convenient one for users who don't want to go through the hassle of selling their former favorite smartphone.