SPG Broadway Sweepstakes is a chance to win 100,000 Starpoints by simply registering your SPG number with Audience Rewards, the official rewards program of Broadway by Sunday August 28. You can earn additional entries and a small number of points by answering trivia questions (20 points or so per answer).
I had planned to write up this offer yesterday just as a last minute opportunity to win some points for a simple sweepstakes registration entry. The promotion has been ongoing for about six weeks now.
Then, I took a look at BoardingArea to see Mommy Points had already written a far more comprehensive piece than I had planned and posted yesterday morning on this same SPG Broadway Sweepstakes promotion. I recommend you read her post for more trivia on this offer.