Taken from the Bing Rewards website:
What is Bing Rewards and how does it work?Bing Rewards gives you opportunities to earn credits redeemable for rewards. Rewards offers may include earning credits for searching on Bing, or trying out new Bing features. Bing Rewards is offered in addition to the Bing search services available to users.
I just started using it and I already have enough points for a free RedBox movie!
Try it out!