I got the following (SPG Gold):
Choose one of the following options:
Earn up to three Free Weekend Nights.
Stay three times between June 1 and August 31, 2007, and get a Free Weekend Night (up to three nights free) when you register by July 15, 2007.
Earn up to 18,000 bonus Starpoints.
Stay three times and earn 3,000 bonus Starpoints®, stay six times and earn 9,000 bonus Starpoints or stay nine times and earn 18,000 bonus Starpoints when you register by July 15, 2007, and stay between June 1 and August 31, 2007.
Haven't decided which yet...