I think the general consensus from Klout detractors is that a single "score" cannot encompass someone's influence. Some people are more influential in certain circles than others.
Of course, there is a broad-based influence score you can apply to people, in the same manner that Super Bowl ads are expensive because they reach a broad-based group of US TV viewers. If Justin Bieber reaches that group better than President Obama, than his higher Klout score is accurate.
But under that assumption, his Klout score (and many other Klout scores) are meaningless because we don't think of ourselves in that context. This is why, for example, HackerNews karma points are not fungible to Reddit's /r/AdviceAnimals karma points.
