I got an email from Xbox.com offering me one months gold membership for free. It seemed to work on multiple accounts so I can't see why it wouldn't work for everyone. Just click the link and remember auto renewal automatically sets to ON, so don't forget to turn it off if you don't want it.
GET YOUR FIRST MONTH OF GOLD FREE
Had fun with your friends during the Free Xbox Live Gold Weekend? Want more? Just sign up to Gold and take your games online, or watch an array of entertainment from the comfort of your own living room – whenever you want!*
You’ve got until 28 May to take advantage of this great Gold deal – get one month of Gold free.**