This has been all over the travel hacking blogs, and early indications are that 1) it is a legit way of getting about 47,000 IHG points (value somewhere between $330-$600 depending on how you spend the points for about $50 in postage supplies but that 2) IHG and Hello World massively underestimated how many people would mail in the allowed 94 envelopes when they were essentially guaranteed 500 points per entry so the AMOE entries are getting returned to mail-in users rather slowly.
Full explanation here:
http://dealswelike.boardingarea.com/2015/11/02/spend-46-and-earn-at-least-47000-ihg-points/
There are some nice IHG options out there under the 'Indigo' flag that are trying to go for a more indie boutique hotel feel instead of generic chain hotel and they often succeed.