We've complained before that the bargain Windows Family Pack only shows up in Australia as a "limited offer" around Christmas. The odds of that ever changing now look very slight, with Microsoft taking the same "offer it then withdraw it" approach elsewhere in the world.
PC World reports that Amazon will stop selling the Family Pack to US customers on December 31. The Australian offer doesn't have an official end date, but seems unlikely to survive much longer. If you do want multiple Windows 7 licences, this is the cheapest way to get them (outside of an enterprise sales deal).
Windows 7 Family Pack Sales to Cease [PC World]