Microsoft tried to nail a guy selling OEM Windows on eBay, and he counter-sued. Microsoft dropped it when it got public and later settled the counter-suit, but kept the terms secret. Microsoft also worked with eBay to have legitimate (even retail shrink-wrapped) auctions of its software pulled, and the resultant ire of the eBay users covered up.
It looks like Microsoft doesn't like first sale, but they don't want to push it through the courts.