that's a bit of a false example there. In the who wants to be a millionaire, the audience has no motivation to twist the truth. They're trying to help the person just as much as their friend. Statistically, you might just choose a friend who doens't know the answer, but the average of a crowd does. I would expect the audience results to be better.
This is not the same as opinion/marketting sites, where there are parties who have an incentive to not provide an honest opinion or to boost their view. You can bet there's political campaigns who would take advantage of opinion sites with their volunteers. Marketting firms have an interest in pumping up their products, even posting fake comments/blogs...There's also a lack of feedback. Suppose restaurant X is recommended by a friend in my facebook network. I can easily follow up with him/her on it. This does yet exist in the wisdom of crowds.
Wisdom of the crowds with 'similar' voting patterns could oversome some of these. That's the old "people who liked this product also like ..." So if I digged one product, it could group me in a crowd with those products...
both are valid methods of ratings/recommendations.
I don't really think facebook is overrated. Maybe we roam in different circles, but I don't hear people raving about facebook. People just treat it as something fairly routine these days; like getting someone's email/phone number...you just add them to facebook.