As posted on Flyertalk:
SPG Better by the Night from October 1 through December 20, 2012. Here is the link and it includes a long list of properties not participating in this promotion.
- Earn double Starpoints on stays of 1 or 2 nights.
- Earn triple Starpoints on stays of 3 nights or more.
- Plus, earn 250 additional bonus Starpoints for stays booked at spg.com, or 500 additional bonus Starpoints for stays booked through the SPG mobile app for iPhone.

For me this is a disappointing promotion. If you are an Android user, as I am, the extra points for the iPhone app is just annoying.