Ian Ayres (former executive editor of The Hilltop and current Yale law prof) and his daughter Anna, spent lots of time writing songs this summer. He'd like a) for you to listen to some of them and b) to gather data. So he's created a contest in which you play three songs - two by Anna and one co-authored by the two of them - and guess which one he co-wrote. The winner gets an iTunes gift card, the value of which is determined by the number of people who view the YouTube clips.
While the contest is open until October 31, he's offering special prizes (i.e., autographed copies of his books) for talented contestants who enter before October 10. I am assuming that regulators will consider this particular challenge a test of skill - thus exempting it from various domestic and foreign regulations of sweepstakes. He must be worried about those pesky regulators since he explicitly notes:
This is not a legally enforceable offer or agreement. While I intend to give someone a gift card, you shouldn’t rely on this post to your detriment. Feel free to say bad things about me though if I don’t pay off.
If you're game to invest eight minutes listening to The Ayres Family Greatest Hits, you can try your luck...uhh, I mean skill... here.