No question it's a privacy matter, but there's nothing stopping you from installing Opinion Rewards and simply not telling it about yourself, it's not like they can validate everything or anything. The survey questions aren't terribly invasive and follow the same consumer marketing themes -- '...do you own a hybrid vehicle...' or '...do you plan on buying one within the next twelve months...' along with just general stuff like your age bracket, favorite music, whatever. If you don't want to give up anything about yourself just think about some second cousin who you haven't seen years who lives five states away, and answer all the questions from their point of view.
Bottom line though, and ignoring the 200 lb. gorilla - our NSA, your ISP/carrier already has more data already collected on you than anything you have to worry about with Opinion Rewards, as everything you do online goes through their pipes. Geez, even this site, along with just regular cookies, includes some tracking cookies. If you use Facebook, you've already lost the battle. If privacy is really important to you, you need to take yourself off the grid and adopt an isolationist lifestyle. (There are those who do and seem pretty damn content with their lives.)