From the University of Toronto:

http://www.psych.utoronto.ca/users/reingold/courses/intelligence/cache/1198gottfred.html

Despite some popular assertions, a single factor for intelligence, called g, can be measured with IQ tests and does predict success in life.

Of course, there are many kinds of talent, many kinds of mental ability and many other aspects of personality and character that influence a person's chances of happiness and success. The functional importance of general mental ability in everyday life, however, means that without onerous restrictions on individual liberty, differences in mental competence are likely to result in social inequality. This gulf between equal opportunity and equal outcomes is perhaps what pains Americans most about the subject of intelligence. The public intuitively knows what is at stake: when asked to rank personal qualities in order of desirability, people put intelligence second only to good health. But with a more realistic approach to the intellectual differences between people, society could better accommodate these differences and minimize the inequalities they create.

Some critics of intelligence research maintain that the notion of general intelligence is illusory: that no such global mental capacity exists and that apparent "intelligence" is really just a by-product of one's opportunities to learn skills and information valued in a particular cultural context. True, the concept of intelligence and the way in which individuals are ranked according to this criterion could be social artifacts. But the fact that g is not specific to any particular domain of knowledge or mental skill suggests that g is independent of cultural content, including beliefs about what intelligence is. And tests of different social groups reveal the same continuum of general intelligence. This observation suggests either that cultures do not construct g or that they construct the same g. Both conclusions undercut the social artifact theory of intelligence.